Avgas/mogas
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Avgas/mogas
Hi all,
I was being asked this question about MOGAS and AVGAS but I was unable to find out why the difference for motor and piston engine aircraft
fuel. I researched on pprune and the net already and what I come to know of is as follows:
I know that:
1. AVGAS is highly refined with very specific Octane ratings
characterizing its resistance to detonation; MOGAS is less refined than AVGAS; it has different octane ratings as well.
2. AVGAS is carefully controlled through supply chain.
3. AVGAS sits longer before going "stale".
3. MOGAS has a higher volatility, lower ignition temperature and
flashpoint, making it more dangerous to handle. Also more prone to vapour lock in the fuel lines as compared to AVGAS.
4. MOGAS has a high lead content. (not sure, what about premium low lead MOGAS??)
I've always known you can't put petrol (MOGAS) into AVGAS engines, but why?? Why we came to choose to use AVGAS as piston engine aircraft fuel; MOGAS as motor car fuel? If MOGAS has similiar octane ratings and actually produces more power (as in horsepower), why don't we use it as piston engine aircraft's fuel? I've read that in choosing a fuel type
(http://www.ausetute.com.au/fuelsdef.html), we consider factors such as energy value, ingnition temperature, volatility, flashpoint, ease of liquifaction and products of combustion. Are higher volatility, lower ignition temperture and lower flashpoint of MOGAS the reasons why we use AVGAS instead of MOGAS?
I've come to learn from here and from other sources that many aircraft engines such as the Lycoming O-320 have been designed for use of the old 80/87 fuel (Similar to gasoline for car). Therefore, the use of MOGAS for the aircraft engines is acceptable. So, again, why some people so strongly advocate NO MOGAS in AVGAS engines? Why create AVGAS to differentiate from MOGAS in the first place?
Moreover, I was very puzzled with the idea put forth:
Cessna C152 has an engine horsepower of 110hp; whereas motor
car/trucks can have horsepower much higher than that of an aircraft like the C152. Why is that so?
After doing some research, I start to figure out it might be due to these reasons.
1. Many of the training aircrafts are even lighter than some cars/trucks. They really don't need as much power (e.g. for speed) as some motors do for what they are designed for - teaching people to fly an aeroplane.
2. Piston-engine aircrafts have different criteria in power generation when compared to cars. Aircrafts need thrust instead of horsepower. As long as the thrust provided is sufficient for the aircraft operations for its design and different flight phases, it's good enough. On the other hand, race cars require high top speed, therefore, more hp to achieve that. Trucks require high torque factor in order to move the high loads on start, therefore, higher hp as well.
Please correct me if I am mistaken in any areas. Thank you very much and a happy flying 2008!
I was being asked this question about MOGAS and AVGAS but I was unable to find out why the difference for motor and piston engine aircraft
fuel. I researched on pprune and the net already and what I come to know of is as follows:
I know that:
1. AVGAS is highly refined with very specific Octane ratings
characterizing its resistance to detonation; MOGAS is less refined than AVGAS; it has different octane ratings as well.
2. AVGAS is carefully controlled through supply chain.
3. AVGAS sits longer before going "stale".
3. MOGAS has a higher volatility, lower ignition temperature and
flashpoint, making it more dangerous to handle. Also more prone to vapour lock in the fuel lines as compared to AVGAS.
4. MOGAS has a high lead content. (not sure, what about premium low lead MOGAS??)
I've always known you can't put petrol (MOGAS) into AVGAS engines, but why?? Why we came to choose to use AVGAS as piston engine aircraft fuel; MOGAS as motor car fuel? If MOGAS has similiar octane ratings and actually produces more power (as in horsepower), why don't we use it as piston engine aircraft's fuel? I've read that in choosing a fuel type
(http://www.ausetute.com.au/fuelsdef.html), we consider factors such as energy value, ingnition temperature, volatility, flashpoint, ease of liquifaction and products of combustion. Are higher volatility, lower ignition temperture and lower flashpoint of MOGAS the reasons why we use AVGAS instead of MOGAS?
I've come to learn from here and from other sources that many aircraft engines such as the Lycoming O-320 have been designed for use of the old 80/87 fuel (Similar to gasoline for car). Therefore, the use of MOGAS for the aircraft engines is acceptable. So, again, why some people so strongly advocate NO MOGAS in AVGAS engines? Why create AVGAS to differentiate from MOGAS in the first place?
Moreover, I was very puzzled with the idea put forth:
Cessna C152 has an engine horsepower of 110hp; whereas motor
car/trucks can have horsepower much higher than that of an aircraft like the C152. Why is that so?
After doing some research, I start to figure out it might be due to these reasons.
1. Many of the training aircrafts are even lighter than some cars/trucks. They really don't need as much power (e.g. for speed) as some motors do for what they are designed for - teaching people to fly an aeroplane.
2. Piston-engine aircrafts have different criteria in power generation when compared to cars. Aircrafts need thrust instead of horsepower. As long as the thrust provided is sufficient for the aircraft operations for its design and different flight phases, it's good enough. On the other hand, race cars require high top speed, therefore, more hp to achieve that. Trucks require high torque factor in order to move the high loads on start, therefore, higher hp as well.
Please correct me if I am mistaken in any areas. Thank you very much and a happy flying 2008!
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4. MOGAS has a high lead content. (not sure, what about premium low lead MOGAS??)
I've always known you can't put petrol (MOGAS) into AVGAS engines, but why?? Why we came to choose to use AVGAS as piston engine aircraft fuel; MOGAS as motor car fuel? If MOGAS has similiar octane ratings and actually produces more power (as in horsepower), why don't we use it as piston engine aircraft's fuel? I've read that in choosing a fuel type
(http://www.ausetute.com.au/fuelsdef.html), we consider factors such as energy value, ingnition temperature, volatility, flashpoint, ease of liquifaction and products of combustion. Are higher volatility, lower ignition temperture and lower flashpoint of MOGAS the reasons why we use AVGAS instead of MOGAS?
(http://www.ausetute.com.au/fuelsdef.html), we consider factors such as energy value, ingnition temperature, volatility, flashpoint, ease of liquifaction and products of combustion. Are higher volatility, lower ignition temperture and lower flashpoint of MOGAS the reasons why we use AVGAS instead of MOGAS?
Auto fuel and avgas are different fuels, and have different properties with respect to aeromatics, effect on fuel system components, the formation of deposits, resistance to detonation (octane), etc. Avgas has a standard which is universal, whereas auto fuel does not, and varies by the batch, and by the refining facility. Further, multiple standards exist by which octane is determined.
Gasoline doesn't produce horsepower. You can compare BTU's per a given unit of fuel, but that alone doesn't equate to horsepower, either. Wringing the last bit of thermal value out of a given measurement of fuel isn't the prime cnocern with the fuel; it's suitability for the powerplant and the application is.
I've come to learn from here and from other sources that many aircraft engines such as the Lycoming O-320 have been designed for use of the old 80/87 fuel (Similar to gasoline for car). Therefore, the use of MOGAS for the aircraft engines is acceptable.
I will say from a maintenance perspective that I've seen a number of carburetors messed up by auto fuel sitting in them for extended periods, whereas I haven't found that to be the case with avgas. I've seen the same thing with other fuel system components. Avgas preserves components such as fuel tank bladders, whereas mogas does not.
Moreover, I was very puzzled with the idea put forth:
Cessna C152 has an engine horsepower of 110hp; whereas motor
car/trucks can have horsepower much higher than that of an aircraft like the C152. Why is that so?
Cessna C152 has an engine horsepower of 110hp; whereas motor
car/trucks can have horsepower much higher than that of an aircraft like the C152. Why is that so?
I've flown the Cessna 150, for example, with an 0-200, and it's an anemic airplane at a mountain field with a student and instructor on board...let's face it, when the takeoff density altitude is nearly 10,000', then that airplane isn't going to impress you much. Put an 0-320 in the same airplane, however, and it does great. I've towed banners the same altitude, flown students all day long, towed gliders, etc...no problem. Same airplane, different powerplants, different performance.
One doesn't go particularly faster than the other, but the climb performance s the telling difference, because excess power translates to climb performance.
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From my own experience the worst carb icing we ever experienced was when using car fuel and CAA confirm their dislike of car fuel for this reason. I understand it vapourises much more easily that aviation fuel which makes it more prone to increase the risk of carb icing
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All U.K. Mogas is unleaded now and has been for some time. Comparing aero piston engines with automotive ones is not easy. The requirements are very different. As most light A/C have fixed pitch propellors, high torque at low rpm is needed - try pulling away in your car in a high gear if you want to know why! The other thing is the ability to deliver full power (or a high percentage of it) indefinitely. Not many cars get driven flat out for hours on end, day after day. Engine failure in a car doesn't usually have the same implications as it would in an aeroplane... The design of the plane can also have a considerable effect on the power required. 100hp pulls 2 people along at around 85 knots in a C150, or 4 people at over 100 knots in a modern design like the Dyn Aero MCR 4S.
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An aircraft engine is required to produce a lot of torque at about 2600 rpm.
This requires a large cylinder design, which is conducive to detonation. To prevent detonation, a high octane fuel is required. AVGAS still has a lot of lead in it. 100/130 LL means "low lead" only in comparison to what the older fuels used to contain and it can't be compared to the amount previously used in MOGAS, it was actually far higher.
Automotive engines are optimised to produce a lot of horsepower and as a result, generally produce less torque at lower rpm. This is achieved by increasing the speed range of the engine (simply speaking, torque x rpm = horsepower).
The extreme end of the range of this type of engine is a Formula 1 car engine. These have multiple, small capacity cylinders which can rev almost ten times as fast as an aircraft engine. A lot of horsepower is produced at the top end of the rev range but one wouldn't pull a 2,600 rpm prop on direct drive; it might not even run at all at that speed. Also, it would cost a fortune and would need an overhaul after tens of hours, rather than hundreds or thousands of an aircraft engine.
This type of engine needs a higher volatility fuel as there is very little time for it to evaporate on its extremely short journey through the inlet port.
Note that modern cars no longer have carburettors - so they cannot suffer from carb icing and there is no current need for a fuel supplier to be concerned about the problem; an old aircraft engine obviously can be badly affected if MOGAS is used.
This requires a large cylinder design, which is conducive to detonation. To prevent detonation, a high octane fuel is required. AVGAS still has a lot of lead in it. 100/130 LL means "low lead" only in comparison to what the older fuels used to contain and it can't be compared to the amount previously used in MOGAS, it was actually far higher.
Automotive engines are optimised to produce a lot of horsepower and as a result, generally produce less torque at lower rpm. This is achieved by increasing the speed range of the engine (simply speaking, torque x rpm = horsepower).
The extreme end of the range of this type of engine is a Formula 1 car engine. These have multiple, small capacity cylinders which can rev almost ten times as fast as an aircraft engine. A lot of horsepower is produced at the top end of the rev range but one wouldn't pull a 2,600 rpm prop on direct drive; it might not even run at all at that speed. Also, it would cost a fortune and would need an overhaul after tens of hours, rather than hundreds or thousands of an aircraft engine.
This type of engine needs a higher volatility fuel as there is very little time for it to evaporate on its extremely short journey through the inlet port.
Note that modern cars no longer have carburettors - so they cannot suffer from carb icing and there is no current need for a fuel supplier to be concerned about the problem; an old aircraft engine obviously can be badly affected if MOGAS is used.
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Comparing aero piston engines with automotive ones is not easy.
In principle I think that any aviation piston engine block (with the obvious exception of Diesels, like Thielert) should be able to run on any gasoline fuel, be it mogas, mogas with alcohol/ethanol added, 100LL, 100 or any of the older aviation fuels.
BUT the devil is in the details:
- Some types of fuel will auto-ignite with lower compression/lower temperatures than others. This might lead to detonation, which may wreck your engine in a matter of seconds. Some engines are more susceptible to this than others. Sometimes proper leaning techniques can help.
- Lead is added to aviation gasoline, and was added to automotive gasoline, for a reason. Part reason is to prevent/delay detonation, but I believe the other reason is in maintaining the seals on the valve seats. The lead in the fuel deposits itself on the valve seats thus maintaining the seal. If you run such an engine on a fuel without lead, after a while your valves start leaking. Not good. Modern engines (such as car engines, or Rotax) use different valve seats which do not rely on the lead in the fuel to maintain a seal.
- As llanfairpg mentioned, if the fuel vaporizes too fast the chances of carb icing are greatly increased. Also, at high altitudes, vapor lock is a problem. Both because of the higher volatility.
- Various fuels have various additives added to it. A fuel system (tanks, lines, valves, pumps, carbs etc) all have to be resistant to these additives.
For all these reasons (and most likely more) the manufacturer of the engine block and the manufacturer of the airframe (which includes the fuel hoses etc) specify certain fuels that can be used, and certain limitations on operations when using certain kinds of fuels. For instance: no high-altitude operations when using mogas, but no restrictions on 100LL. All this will be in the POH. If new fuels come onto the market (such as lead-free mogas quite some years ago, and mogas with biofuel/ethanol added right now), the manufacturer may provide a Supplemental Type Certificate (in essence an addition to the POH) so that this new fuel may be used. It may also stipulate conditions such as replacement of certain components before the new fuel can be used.
As far as power output is concerned: the mechanical characteristics of the engine, including bore and stroke, determine the "torque curve": the maximum amount of torque an engine can deliver, on a certain fuel, at a certain RPM. The power output of the engine is a direct derivative from that: P = 2 * pi * T * R, where P = Power in Watts, T = Torque in Nm and R = rotation speed in RPS (rounds per second). (Use the appropriate conversion factors to get to non-SI values, such as HP instead of Watt.)
In a car, the exact torque curve and where it reaches peak torque doesn't matter all that much, since you have a number of gears to match your current speed with the engine RPM for top performance. The same can be achieved in aero applications with internal reduction drives (Rotax, Thielert) and VP/CS propellors. Without a reduction drive, such as with the direct drive Continentals and Lycomings, the crankshaft RPM is the same as propshaft RPM, and thus limited by the need for the prop tips to remain subsonic. So the highest RPM that these engines should be able to sustain is around 2700. Hence their relatively large internal displacements: 3.8 liters displacement in a flat four to generate 120 horsepower (O-235 as in the DR200-120) is something that the automotive industry laughs about. But they're not limited to 2700 rpm. For comparison, the Rotax 912 does 100 HP with a displacement of just 1.35 liters, at 5800 RPM. The 1:2.43 reduction drive reduces that to a prop RPM of about 2400 RPM.
Within that limited range of, let's say, 1000 RPM (idle) and 2700 RPM (redline), all the aircraft operations need to take place. For relatively low speed (up to about 100 knots) that's fine on a fixed pitch prop, but to become more efficient at all flight regimes, a VP or CS prop is required.
At the end of it all it's the horsepowers the engine delivers, and the way these are transferred onto the medium you use for propulsion (road or air) that determine the performance. If you're at the cruise and you have excess horsepowers to spare, you can use these to accellerate or to climb. In airplane speak, this is "excess thrust".
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In principle I think that any aviation piston engine block (with the obvious exception of Diesels, like Thielert) should be able to run on any gasoline fuel, be it mogas, mogas with alcohol/ethanol added, 100LL, 100 or any of the older aviation fuels.
Mogas isnt monitored or tested to the same standards as Avgas and its vapourisation rate can increase carb icing problems and fuel pump problems.
CAA Air Safety Sense lealet no 4 should be read before using mogas
There are various threads on Prune and in "another place" about how appalling out of date current production Lycoming and Continental GA engines are so I won't revisit that theme.
One important safety point, hinted at in the post above, which should be made clear to anyone wanting to swap fuels without due care and attention. Apart from the valve system wear issue of zero lead gasoline, which is at least slow in its effects so may not kill you, it is important to realise that pump fuel is not pure gasoline and different fuel mixes have different additives which may cause rapid and potentially catastrophic failures in items such as seals and diaphragms. By way of example, back in the early nineties, I was involved with developing an engine for Brazil where the fuel has a very high alcohol content (80% ethanol IIRC). We had test bed fires when pressure regulator diaphragms designed for US / Europe gasoline burst after exposure to Brazilian high alcohol fuel. I have been out of the car business for a few years now but believe that European road gasoline has a percentage (10% ? ) of alcohol these days.
One important safety point, hinted at in the post above, which should be made clear to anyone wanting to swap fuels without due care and attention. Apart from the valve system wear issue of zero lead gasoline, which is at least slow in its effects so may not kill you, it is important to realise that pump fuel is not pure gasoline and different fuel mixes have different additives which may cause rapid and potentially catastrophic failures in items such as seals and diaphragms. By way of example, back in the early nineties, I was involved with developing an engine for Brazil where the fuel has a very high alcohol content (80% ethanol IIRC). We had test bed fires when pressure regulator diaphragms designed for US / Europe gasoline burst after exposure to Brazilian high alcohol fuel. I have been out of the car business for a few years now but believe that European road gasoline has a percentage (10% ? ) of alcohol these days.
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I had great success over the years operating a number of aircraft on Mogas. I did all of the evaluation and testing required to convert a TCM IO-520D to be carburetted, and approve it to use Mogas in a Cessna 185. This was a complete success, and the aircraft flew for many years this way with no limitations. It ceased flying only due to pilot error, nothing to do with the fuel.
There are some engine/airframe combinations which cannot handle Mogas safely, and experimentation is a bad idea. If it is approved, get the approval, and follow the instructions. If it's not approved by now, forget it, it won't be worth the effort to approve it, even if it is possible.
My total flying experience on Mogas exceeds 3500 hours, as high as 20,000', and at temperatures exceeding 100F. I have been careful, and never had any unfavourable event associated with Mogas use.
In my Cessna 150, it is extremely better than 100LL in terms of not sticking exhaust valves. A former Cessna employee whom I knew, also a 150 owner, was a real proponent of Mogas, because of his experience with valve problems in his plane. He taught me a lot about this, and authored a very good book on the subject.
Avgas and Mogas differ in many ways. One important way is that Mogas is a blend of many different liquids to create the desired properties, where Avgas is only one liquid. This is why when Mogas evaporates, gum is often left. Think of it as the difference between clean water and a soft drink. When the water evaporates, it's all gone and the glass is clean and dry. when a soft drink evaporates, it goes flat first (very volatile parts gone first) once this happens to Mogas, starting is more difficult (stale gas) but there's still liquid there, once that liquid evaporates, gum is left. Adding fresh gas gets things right again. You'll notice that when Avgas evaporates, it all goes at once, and only a dry (poisonous) film is left.
Refer to Transport Canada's publication TP10737, it has a lot of useful information.
What follows is a cut and paste of an article I wrote on this subject 15 years ago:
Pilot DAR
GASOLINE AND YOUR ENGINE
Gasoline is one of those things we use so much of, we really seem to take it for granted. Certainly, with the exception of water from time to time, gasoline is a very reliable aviation product- it just about always does what it is supposed to. During the years when we flew on Avgas only, we really took it for granted. Now, with the wide spread use of Mogas, we are paying a bit more attention. It is a widely agreed statistic that
the users of Mogas have far fewer cases of running out of gas in flight. This has been attributed to the simple fact that those pilots were more aware of their fuel situation. There were probably cases where a particular aircraft was not approved for that fuel, and the forced landing might attract unwanted attention to the use of Mogas.
At present, with the exception of 80/87, we have the greatest choice of gasolines, suppliers, and prices that we have ever had. To help with this choice, a bit of information about how certain characteristics of gasoline affect your engine may be of some help. The major factors which make Mogas different from Avgas center around volatility and Octane Rating, Leadis an important, but smaller issue.
Volatility
The volatility is a measure of the fuel's ease of evaporation in the prevailing atmospheric conditions. The volatility of Avgas is kept constant all year, for all geographic locations. The volatility of Mogas is changed to suit both the season, and location of point of sale. A high volatility gasoline will make the engine easier to start, but more likely to vapour lock after it is running. Vapour lock is the boiling, or evaporation, of the gasoline in the fuel system. The fuel vapour is not enough fuel for the engine to run , so it stops, and is very hard to restart until it cools. Automotive consumers of gasoline have, over the years, demanded cars that will start, and keep running, all year around. The gasoline manufacturers responded by creating a system whereby the volatility is changed as appropriate for the climate. When this then created vapour lock problems in some cars, fuel system designs were changed to eliminate that problem. Nearly all cars now have the fuel pump in, or very near the gas tank. This keeps the entire fuel system under considerable pressure, and eliminates vapour lock.
Why not change aircraft fuel systems to this design to eliminate the vapour lock risk? Four reasons: Redesigning, and reworking anything on an airplane is costly and time consuming, and the need, in this case, is great enough. Secondly, for carburetor equipped aircraft, the carb cannot withstand the high fuel system pressure (most carbs are happy from 1 to 5 PSI), which would be required to eliminate vapour lock. Thirdly, for injected aircraft, the engine relies on a pressure fuel system, if we put electric pumps out at the tanks, and have an electrical failure, we are going to loose fuel pressure and have an engine failure. The engine driven fuel pump is an important part of safe flight. Last important reason: Unlike cars, aircraft fuel lines run inside the cabin. If a line or fitting failed, would you want high pressure fuel spraying around the cabin?
Page 2
The concerns about the volatility of Mogas as it applies to safe flight, have been well addressed, and very thoroughly tested. You can be sure that as long as you use the gasoline of the season, as directed by the conditions of the STC, you will be as safe as if you were using Avgas. A move toward a cleaner environment ( less fuel vapour in the air from evaporating supplies) will see Mogas volatility being gradually reduced in the years to come. In the mean time: Use gasoline purchased from a reputable supplier during the season in which it was purchased. DO NOT use gasoline purchased in the winter, during the warm spring and summer. Ensure that full power is available early in the takeoff, and if you are still concerned on a really hot day, mix in some 100LL.
Octane
Octane is actually a liquid which can be used as a fuel. If used as a fuel in its pure form, it would have an Octane Rating of exactly 100, and flying would be really expensive! To reduce the cost of flying for us, the gasoline manufacturers blend other much cheaper liquids to create a gasoline which is suitable for use. The anti-knock qualities of this fuel are compared to that of Octane, and a numerical "rating" given. The elements which increase Octane Rating are very expensive (like Octane itself), and are not needlessly added, so you can count on the Octane Rating of the gasoline you buy, being very accurate. Tetra-Ethyl Lead is also used to boost Octane Rating, more on that later.
If the Octane Rating of the gasoline you are using is too low, detonation is a risk.
Detonation is most easily described as ignition of the gasoline vapour prior to spark plug firing. It is only likely to occur at full throttle. Any power setting less than full throttle reduces the factors which promote detonation. The effects of detonation can be anywhere from not detectable, to immediately destructive.
It is well understood that engines run best when the timing of the spark plug firing is actually matched to the ideal position of the piston as it rises in the compression stroke. Too late (lower timing angle), and the engine develops noticeably less power, and is at greater risk of detonation. Too early (higher timing angle), and the engine may develop a bit more power, but it is under much greater strain due to increased cylinder pressures. This can be explained by understanding that though brief, it does take time for the fuel/air mixture to burn in the cylinder. Only after the mixture is completely burned, is the desired explosive pressure achieved. It is very desirable to have this peak explosive pressure occur exactly at the time when the piston is just beginning to go down the power stroke. This is where the power comes from! If this peak pressure occurs too early in the stroke, it actually applies a braking force to the rising piston, robbing power, and then the pressure is depleted when the piston finally reaches the power stroke, again, robbing power.
Page 3
In this regard, both very advanced timing, and detonation can be seen to rob power, and apply excess strain on the engine. Detonation, however, has the added danger of allowing combustion to begin in an area of the combustion chamber which was not designed to withstand it. How can that be, you might ask? Consider that the source of ignition is supposed to be the spark plugs. They are positioned in such a way so as to ensure that the flame front radiates outward evenly. This ball of fire is actually surrounded by a wall of unburned fuel which cools it as it contacts the cylinder and piston. This unburned fuel is there because at full power, with the mixture full rich, there is too much fuel for the oxygen present, and without oxygen the fuel won't burn, so it is just there to cool the combustion chamber. You can lean at lower power settings because you are developing less power so there is less total heat, and cooling is not required. If the flame front begins at a point other than intended, or that cooling rich mixture is not there, very hot flame can impinge on the bare aluminum of the cylinder head or the piston top. Flame temperatures can reach 4000 F, aluminum melts at about 1300 F.
Detonation can only be detected in the cockpit by a loss of power and an indication of high cylinder head temperature, both of which will only be obvious only after the damage has begun. Detonation testing for engine approval is a complicated process which involves deliberately causing the engine to detonate to prove you can detect it, and then testing the subject gasoline to prove that not only does it not detonate, but there is a good margin between normal operating conditions, and those conditions which might result in detonation. The conditions which might promote detonation include: high ambient air temperature, high cylinder head temperature, high power, low engine speed (running a constant speed prop "over square", and low Octane gasoline.
You can eliminate the risk of detonation by keeping you engine running as cool as possible, ensuring that you are using gasoline with an Octane Rating which meets the manufacturer's requirements, and if your engine has a constant speed prop, keeping the RPM high. In normally aspirated engines, there should never be a need to run the Manifold Pressure in inches higher than the RPM in hundreds. When you reduce power, reduce the throttle first, then the prop.
Tetra-Ethyl Lead
"Lead" is used mainly to boost Octane. The effect of the lead in this regard is to reduce the gasoline's likelihood to ignite before the spark hits it. Lead does not increase the power at all, instead, it allows the use of higher compression ratios in engine design, which will give you more power from the same size engine. Tetra-Ethyl Lead has been found to be very bad for our heath, and the environment. This has resulted in it having been banned in all gasolines except Avgas. The lead in Avgas was reduced by half, which resulted in 100LL, but there is still a lot of Lead in 100LL. Like other Octane boosters, Lead is expensive, and is only added if it is needed. 100LL must have Lead to meet the Octane Rating, but 80/87 usually does not need Lead at all. Most of the 80/87 you might have ever purchased, probably did not have any lead at all. Lead is permitted in 80/87 to allow for intermixing with 100/130 during handling and transport. Some manufacturers of 80/87 are reported to have added some Lead at times, but not to the limits allowed.
Page 4
The use of 100LL in engines originally designed for 80/87 is encouraged by the Avgas manufacturers primarily to reduce the demand for 80/87, which they no longer want to manufacture. 100/130 was always an approved alternate fuel for these low compression engines, but never the preferred fuel. 100LL meets the performance requirements for 100/130 so it was substituted. Somewhere along the line, some people forgot that all that Lead really doesn't work well in low compression engines. These engines just don't have the extreme operating temperatures and pressures to burn off lots of lead . The result is often fouled spark plugs, sticking exhaust valves, and sticking piston rings. These problems go from a nuisance, to very costly and unsafe. The use of Mogas has defiantly eliminated these problems for many pilots.
A small amount of Lead has the beneficial effect of providing a protective coating on the exhaust valves. This coating dramatically reduces erosion of the valve face and seat, and the wear of the guide. Aircraft which have operated for hundreds of hours on only Mogas have sometimes been found to have such valve wear. For aircraft which had even small amounts of 100LL at times ( one in twenty fillups), the wear was noticeably reduced. Recent testing with special additives has produced excellent results in regard to eliminating this early valve damage. This additive can be added to the gasoline at any point, is very safe to use, and is added in such small quantities that it does not take the gasoline off specification. Approval of this product is currently underway with Transport Canada, but because the amount used is so small, it will probably be difficult for Transport to disapprove.
In Summary:
For engines originally designed to use 80/87, usually any of the other gasolines will work, but each has drawbacks if used exclusively. Choose a gasoline which is approved for use in your airplane and engine. Regardless of what type it is, ensure that it is handled safely, and protected from contamination. If you choose to use Mogas, buy it from a reputable supplier, and use it during the season in which it was purchased. If you have a larger engine with a constant speed prop, at times when you are at or near full power, avoid power settings with a high manifold pressure and low RPM. If you are operating on a very hot day, take steps to keep the fuel cool: Refuel just before takeoff (in-ground tanks keep the gasoline quite cool), park in the shade. If you have just landed, leave cowl flaps open, and open the oil door on the cowl to let out heat. In all cases, ensure that full power is available early in the takeoff.
You may have noticed that gasoline and oil are among the very few things that you service your plane with, which are not specifically signed off as being airworthy before you fly with them, take the responsibility yourself, because it matters to you.
There are some engine/airframe combinations which cannot handle Mogas safely, and experimentation is a bad idea. If it is approved, get the approval, and follow the instructions. If it's not approved by now, forget it, it won't be worth the effort to approve it, even if it is possible.
My total flying experience on Mogas exceeds 3500 hours, as high as 20,000', and at temperatures exceeding 100F. I have been careful, and never had any unfavourable event associated with Mogas use.
In my Cessna 150, it is extremely better than 100LL in terms of not sticking exhaust valves. A former Cessna employee whom I knew, also a 150 owner, was a real proponent of Mogas, because of his experience with valve problems in his plane. He taught me a lot about this, and authored a very good book on the subject.
Avgas and Mogas differ in many ways. One important way is that Mogas is a blend of many different liquids to create the desired properties, where Avgas is only one liquid. This is why when Mogas evaporates, gum is often left. Think of it as the difference between clean water and a soft drink. When the water evaporates, it's all gone and the glass is clean and dry. when a soft drink evaporates, it goes flat first (very volatile parts gone first) once this happens to Mogas, starting is more difficult (stale gas) but there's still liquid there, once that liquid evaporates, gum is left. Adding fresh gas gets things right again. You'll notice that when Avgas evaporates, it all goes at once, and only a dry (poisonous) film is left.
Refer to Transport Canada's publication TP10737, it has a lot of useful information.
What follows is a cut and paste of an article I wrote on this subject 15 years ago:
Pilot DAR
GASOLINE AND YOUR ENGINE
Gasoline is one of those things we use so much of, we really seem to take it for granted. Certainly, with the exception of water from time to time, gasoline is a very reliable aviation product- it just about always does what it is supposed to. During the years when we flew on Avgas only, we really took it for granted. Now, with the wide spread use of Mogas, we are paying a bit more attention. It is a widely agreed statistic that
the users of Mogas have far fewer cases of running out of gas in flight. This has been attributed to the simple fact that those pilots were more aware of their fuel situation. There were probably cases where a particular aircraft was not approved for that fuel, and the forced landing might attract unwanted attention to the use of Mogas.
At present, with the exception of 80/87, we have the greatest choice of gasolines, suppliers, and prices that we have ever had. To help with this choice, a bit of information about how certain characteristics of gasoline affect your engine may be of some help. The major factors which make Mogas different from Avgas center around volatility and Octane Rating, Leadis an important, but smaller issue.
Volatility
The volatility is a measure of the fuel's ease of evaporation in the prevailing atmospheric conditions. The volatility of Avgas is kept constant all year, for all geographic locations. The volatility of Mogas is changed to suit both the season, and location of point of sale. A high volatility gasoline will make the engine easier to start, but more likely to vapour lock after it is running. Vapour lock is the boiling, or evaporation, of the gasoline in the fuel system. The fuel vapour is not enough fuel for the engine to run , so it stops, and is very hard to restart until it cools. Automotive consumers of gasoline have, over the years, demanded cars that will start, and keep running, all year around. The gasoline manufacturers responded by creating a system whereby the volatility is changed as appropriate for the climate. When this then created vapour lock problems in some cars, fuel system designs were changed to eliminate that problem. Nearly all cars now have the fuel pump in, or very near the gas tank. This keeps the entire fuel system under considerable pressure, and eliminates vapour lock.
Why not change aircraft fuel systems to this design to eliminate the vapour lock risk? Four reasons: Redesigning, and reworking anything on an airplane is costly and time consuming, and the need, in this case, is great enough. Secondly, for carburetor equipped aircraft, the carb cannot withstand the high fuel system pressure (most carbs are happy from 1 to 5 PSI), which would be required to eliminate vapour lock. Thirdly, for injected aircraft, the engine relies on a pressure fuel system, if we put electric pumps out at the tanks, and have an electrical failure, we are going to loose fuel pressure and have an engine failure. The engine driven fuel pump is an important part of safe flight. Last important reason: Unlike cars, aircraft fuel lines run inside the cabin. If a line or fitting failed, would you want high pressure fuel spraying around the cabin?
Page 2
The concerns about the volatility of Mogas as it applies to safe flight, have been well addressed, and very thoroughly tested. You can be sure that as long as you use the gasoline of the season, as directed by the conditions of the STC, you will be as safe as if you were using Avgas. A move toward a cleaner environment ( less fuel vapour in the air from evaporating supplies) will see Mogas volatility being gradually reduced in the years to come. In the mean time: Use gasoline purchased from a reputable supplier during the season in which it was purchased. DO NOT use gasoline purchased in the winter, during the warm spring and summer. Ensure that full power is available early in the takeoff, and if you are still concerned on a really hot day, mix in some 100LL.
Octane
Octane is actually a liquid which can be used as a fuel. If used as a fuel in its pure form, it would have an Octane Rating of exactly 100, and flying would be really expensive! To reduce the cost of flying for us, the gasoline manufacturers blend other much cheaper liquids to create a gasoline which is suitable for use. The anti-knock qualities of this fuel are compared to that of Octane, and a numerical "rating" given. The elements which increase Octane Rating are very expensive (like Octane itself), and are not needlessly added, so you can count on the Octane Rating of the gasoline you buy, being very accurate. Tetra-Ethyl Lead is also used to boost Octane Rating, more on that later.
If the Octane Rating of the gasoline you are using is too low, detonation is a risk.
Detonation is most easily described as ignition of the gasoline vapour prior to spark plug firing. It is only likely to occur at full throttle. Any power setting less than full throttle reduces the factors which promote detonation. The effects of detonation can be anywhere from not detectable, to immediately destructive.
It is well understood that engines run best when the timing of the spark plug firing is actually matched to the ideal position of the piston as it rises in the compression stroke. Too late (lower timing angle), and the engine develops noticeably less power, and is at greater risk of detonation. Too early (higher timing angle), and the engine may develop a bit more power, but it is under much greater strain due to increased cylinder pressures. This can be explained by understanding that though brief, it does take time for the fuel/air mixture to burn in the cylinder. Only after the mixture is completely burned, is the desired explosive pressure achieved. It is very desirable to have this peak explosive pressure occur exactly at the time when the piston is just beginning to go down the power stroke. This is where the power comes from! If this peak pressure occurs too early in the stroke, it actually applies a braking force to the rising piston, robbing power, and then the pressure is depleted when the piston finally reaches the power stroke, again, robbing power.
Page 3
In this regard, both very advanced timing, and detonation can be seen to rob power, and apply excess strain on the engine. Detonation, however, has the added danger of allowing combustion to begin in an area of the combustion chamber which was not designed to withstand it. How can that be, you might ask? Consider that the source of ignition is supposed to be the spark plugs. They are positioned in such a way so as to ensure that the flame front radiates outward evenly. This ball of fire is actually surrounded by a wall of unburned fuel which cools it as it contacts the cylinder and piston. This unburned fuel is there because at full power, with the mixture full rich, there is too much fuel for the oxygen present, and without oxygen the fuel won't burn, so it is just there to cool the combustion chamber. You can lean at lower power settings because you are developing less power so there is less total heat, and cooling is not required. If the flame front begins at a point other than intended, or that cooling rich mixture is not there, very hot flame can impinge on the bare aluminum of the cylinder head or the piston top. Flame temperatures can reach 4000 F, aluminum melts at about 1300 F.
Detonation can only be detected in the cockpit by a loss of power and an indication of high cylinder head temperature, both of which will only be obvious only after the damage has begun. Detonation testing for engine approval is a complicated process which involves deliberately causing the engine to detonate to prove you can detect it, and then testing the subject gasoline to prove that not only does it not detonate, but there is a good margin between normal operating conditions, and those conditions which might result in detonation. The conditions which might promote detonation include: high ambient air temperature, high cylinder head temperature, high power, low engine speed (running a constant speed prop "over square", and low Octane gasoline.
You can eliminate the risk of detonation by keeping you engine running as cool as possible, ensuring that you are using gasoline with an Octane Rating which meets the manufacturer's requirements, and if your engine has a constant speed prop, keeping the RPM high. In normally aspirated engines, there should never be a need to run the Manifold Pressure in inches higher than the RPM in hundreds. When you reduce power, reduce the throttle first, then the prop.
Tetra-Ethyl Lead
"Lead" is used mainly to boost Octane. The effect of the lead in this regard is to reduce the gasoline's likelihood to ignite before the spark hits it. Lead does not increase the power at all, instead, it allows the use of higher compression ratios in engine design, which will give you more power from the same size engine. Tetra-Ethyl Lead has been found to be very bad for our heath, and the environment. This has resulted in it having been banned in all gasolines except Avgas. The lead in Avgas was reduced by half, which resulted in 100LL, but there is still a lot of Lead in 100LL. Like other Octane boosters, Lead is expensive, and is only added if it is needed. 100LL must have Lead to meet the Octane Rating, but 80/87 usually does not need Lead at all. Most of the 80/87 you might have ever purchased, probably did not have any lead at all. Lead is permitted in 80/87 to allow for intermixing with 100/130 during handling and transport. Some manufacturers of 80/87 are reported to have added some Lead at times, but not to the limits allowed.
Page 4
The use of 100LL in engines originally designed for 80/87 is encouraged by the Avgas manufacturers primarily to reduce the demand for 80/87, which they no longer want to manufacture. 100/130 was always an approved alternate fuel for these low compression engines, but never the preferred fuel. 100LL meets the performance requirements for 100/130 so it was substituted. Somewhere along the line, some people forgot that all that Lead really doesn't work well in low compression engines. These engines just don't have the extreme operating temperatures and pressures to burn off lots of lead . The result is often fouled spark plugs, sticking exhaust valves, and sticking piston rings. These problems go from a nuisance, to very costly and unsafe. The use of Mogas has defiantly eliminated these problems for many pilots.
A small amount of Lead has the beneficial effect of providing a protective coating on the exhaust valves. This coating dramatically reduces erosion of the valve face and seat, and the wear of the guide. Aircraft which have operated for hundreds of hours on only Mogas have sometimes been found to have such valve wear. For aircraft which had even small amounts of 100LL at times ( one in twenty fillups), the wear was noticeably reduced. Recent testing with special additives has produced excellent results in regard to eliminating this early valve damage. This additive can be added to the gasoline at any point, is very safe to use, and is added in such small quantities that it does not take the gasoline off specification. Approval of this product is currently underway with Transport Canada, but because the amount used is so small, it will probably be difficult for Transport to disapprove.
In Summary:
For engines originally designed to use 80/87, usually any of the other gasolines will work, but each has drawbacks if used exclusively. Choose a gasoline which is approved for use in your airplane and engine. Regardless of what type it is, ensure that it is handled safely, and protected from contamination. If you choose to use Mogas, buy it from a reputable supplier, and use it during the season in which it was purchased. If you have a larger engine with a constant speed prop, at times when you are at or near full power, avoid power settings with a high manifold pressure and low RPM. If you are operating on a very hot day, take steps to keep the fuel cool: Refuel just before takeoff (in-ground tanks keep the gasoline quite cool), park in the shade. If you have just landed, leave cowl flaps open, and open the oil door on the cowl to let out heat. In all cases, ensure that full power is available early in the takeoff.
You may have noticed that gasoline and oil are among the very few things that you service your plane with, which are not specifically signed off as being airworthy before you fly with them, take the responsibility yourself, because it matters to you.
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Excellent stuff--it was the winter mogas that gave us very bad carb icing problems in the C152
By the way I dont know if anyone has mentioned it but you smell mogas straight away, or I can anyway, in an aircraft tank
By the way I dont know if anyone has mentioned it but you smell mogas straight away, or I can anyway, in an aircraft tank
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I have been out of the car business for a few years now but believe that European road gasoline has a percentage (10% ? ) of alcohol these days.
At least, that's what I understand the issue to be.
Avoid imitations
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An excellent screed, Pilot DAR!
I would slightly disagree with the description of detonation though. The phenomena of the mixture igniting without, or before a spark occuring is effectively "dieselling", or pre-ignition and if it were to occur, it might result in an engine continuing to run after the ignition were switched off. This can certainly occur in some engines, and some carburettors have an anti-dieselling valve fitted to the idle jet, to simultaneously block the fuel supply when the ignition is switched off, to prevent it.
Detonation is a slightly different phenomena. The fuel air mixture should normally burn outwards from the spark plug nose(s), on a flame "front", resulting in a rapid pressure rise in the combustion chamber. The maximum pressure should occur at approximately 17 degrees after top dead centre. However, if this pressure rise is too rapid and too high, the remaining mixture ahead of the flame front can get to a point where it will spontaneously explode, rather than continuing to burn normally. This is detonation.
This is why an engine at low rpm is likely to detonate more readily, as is a larger engine. This is also why rich mixture helps prevent detonation, the flame front travels slower because there is less oxygen (more fuel there instead) and the evaporating "extra" fuel keeps the gases slightly cooler.
(Water injection does a similar job to a rich mixture).
Obviously, aircraft engines are relatively slow turning and have large cylinders. That's why they need high quality fuel and careful handling.
A historical point, the higher of the two figures e.g. 100/130 relates to the equivalent octane at rich mixture, which was highly relevant to supercharged engines when this designation first came into general use in WWII.
I would slightly disagree with the description of detonation though. The phenomena of the mixture igniting without, or before a spark occuring is effectively "dieselling", or pre-ignition and if it were to occur, it might result in an engine continuing to run after the ignition were switched off. This can certainly occur in some engines, and some carburettors have an anti-dieselling valve fitted to the idle jet, to simultaneously block the fuel supply when the ignition is switched off, to prevent it.
Detonation is a slightly different phenomena. The fuel air mixture should normally burn outwards from the spark plug nose(s), on a flame "front", resulting in a rapid pressure rise in the combustion chamber. The maximum pressure should occur at approximately 17 degrees after top dead centre. However, if this pressure rise is too rapid and too high, the remaining mixture ahead of the flame front can get to a point where it will spontaneously explode, rather than continuing to burn normally. This is detonation.
This is why an engine at low rpm is likely to detonate more readily, as is a larger engine. This is also why rich mixture helps prevent detonation, the flame front travels slower because there is less oxygen (more fuel there instead) and the evaporating "extra" fuel keeps the gases slightly cooler.
(Water injection does a similar job to a rich mixture).
Obviously, aircraft engines are relatively slow turning and have large cylinders. That's why they need high quality fuel and careful handling.
A historical point, the higher of the two figures e.g. 100/130 relates to the equivalent octane at rich mixture, which was highly relevant to supercharged engines when this designation first came into general use in WWII.
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Wish I had known many years ago what I now know after reading this thread.
Once had the left wing tank of a Wirraway/(T6 equivalent) topped up by mistake with jet fuel. Engine started OK with neat Avgas in the carby but soon started to exhaust clouds of grey smoke and then refused to run with a manifold pressure greater than 15". Much backfiring.
It would have been diabolical to have flown on the right tank first and then started to use the mix of avgas and jetfuel from the L tank.
Problem was difficult to diagnose. A carby change was useless. Fuel in both tanks smelled the same. Clue to probem came when engineer dipped a finger into fuel in L tank. Seemed OK initially but soon the high volatile portion of the finger sample had evaporated leaving behind the oily residue of the jet fuel and a smell of kerosene.
Engine, which should have been rejected, subsequently had a piston failure followed by a successful forced landing.
Once had the left wing tank of a Wirraway/(T6 equivalent) topped up by mistake with jet fuel. Engine started OK with neat Avgas in the carby but soon started to exhaust clouds of grey smoke and then refused to run with a manifold pressure greater than 15". Much backfiring.
It would have been diabolical to have flown on the right tank first and then started to use the mix of avgas and jetfuel from the L tank.
Problem was difficult to diagnose. A carby change was useless. Fuel in both tanks smelled the same. Clue to probem came when engineer dipped a finger into fuel in L tank. Seemed OK initially but soon the high volatile portion of the finger sample had evaporated leaving behind the oily residue of the jet fuel and a smell of kerosene.
Engine, which should have been rejected, subsequently had a piston failure followed by a successful forced landing.
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Dunno about the -360, but the -320 (in the PA28-161) produces 160 HP at 2700 RPM. That's 119 kW at 45 RPS. So torque at that setting would be 119.000/2.pi.45 = 420 Nm
Maximum torque isn't always reached at the highest RPM though. There may be an RPM below 2700 which produces more torque than that, but because of the lower RPMs, produces less HP overall. You'd have to consult the torque diagram of the engine for that. Not a standard part of a POH, I'm afraid. Have to find a data sheet for the engine.
Maximum torque isn't always reached at the highest RPM though. There may be an RPM below 2700 which produces more torque than that, but because of the lower RPMs, produces less HP overall. You'd have to consult the torque diagram of the engine for that. Not a standard part of a POH, I'm afraid. Have to find a data sheet for the engine.
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Yes Shy Torque,
I agree that the term "detonation" can be applied differently, and I agree with your distinctions. The article was written with the term being applied in its meaning as provided in standard 33.47, where it's meaning is pretty broad. Although, particularly in the automotive world, there are distinctions in the circumstances of gasoline igniting other than intended, in aircraft engine design, these undesired events seem to be all lumped into one definition: Gasoline igniting at a time and/or place other than by spark ignition, and the associated non-standard flame front.
When testing to show the engine can be consistantly operated free of detonation through the defined operating range, it is necessary to deliberately detonate the engine to prove that it would be detected when it occurs during the testing. Surprisingly, after it has been produced and detected, a reduction of power does not immediately remove the damaging affects. Temperatures can still run away, and even when you know it's happening, the pilot is powerless (pun intended) to stop it on command. (Uh oh! aircraft commander! Sorry, that was another thread!).
When considering the relative octane rating (setting aside for the moment the "RON+MON" calculation), any Mogas in the "western" world willl have a minimum octane of around 87, where the old 80/87 had a minimum octane of 80. That makes Mogas a safe bet for low compression aircraft engine use from an octane standpoint. It was necessary to run the higher compression IO-520 engine on 80/87, and even then, way "over square" to get it to detonate during the testing.
The introduction of "oxygenates", which are generally alcohols, is becoming common, and will have some undesired affects on aircraft fuel systems. D not use such gasoline without approval. We did have success running a modified Cessna 150, with a slightly modified O-200 engine on pure ethanol for a few years, but the certification hurtles associated with this were too much to overcome, so the project was abandoned. It ran well and we flew a few hundred hours, but you smelled like a drunk when you were done flying!
Cheers, Pilot DAR
I agree that the term "detonation" can be applied differently, and I agree with your distinctions. The article was written with the term being applied in its meaning as provided in standard 33.47, where it's meaning is pretty broad. Although, particularly in the automotive world, there are distinctions in the circumstances of gasoline igniting other than intended, in aircraft engine design, these undesired events seem to be all lumped into one definition: Gasoline igniting at a time and/or place other than by spark ignition, and the associated non-standard flame front.
When testing to show the engine can be consistantly operated free of detonation through the defined operating range, it is necessary to deliberately detonate the engine to prove that it would be detected when it occurs during the testing. Surprisingly, after it has been produced and detected, a reduction of power does not immediately remove the damaging affects. Temperatures can still run away, and even when you know it's happening, the pilot is powerless (pun intended) to stop it on command. (Uh oh! aircraft commander! Sorry, that was another thread!).
When considering the relative octane rating (setting aside for the moment the "RON+MON" calculation), any Mogas in the "western" world willl have a minimum octane of around 87, where the old 80/87 had a minimum octane of 80. That makes Mogas a safe bet for low compression aircraft engine use from an octane standpoint. It was necessary to run the higher compression IO-520 engine on 80/87, and even then, way "over square" to get it to detonate during the testing.
The introduction of "oxygenates", which are generally alcohols, is becoming common, and will have some undesired affects on aircraft fuel systems. D not use such gasoline without approval. We did have success running a modified Cessna 150, with a slightly modified O-200 engine on pure ethanol for a few years, but the certification hurtles associated with this were too much to overcome, so the project was abandoned. It ran well and we flew a few hundred hours, but you smelled like a drunk when you were done flying!
Cheers, Pilot DAR
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AVGAS is described in ; http://www.dstan.mod.uk/data/91/090/00000200.pdf
Regrettably, CIVGAS (or MOGAS then ULGAS) is no longer covered by a DEFSTAN. Even more regrettably, Mr Thicky, here, never kept a copy of it to show the spec.
I would say your biggest enemy, apart from loss of lead lubrication and cushioning of valves, is the corrosive action on many seals, diaphragms and sealants. Unleaded fuel was one of the first really successful "green" con tricks of the last Century. Let's not mention combustion products.
Regrettably, CIVGAS (or MOGAS then ULGAS) is no longer covered by a DEFSTAN. Even more regrettably, Mr Thicky, here, never kept a copy of it to show the spec.
I would say your biggest enemy, apart from loss of lead lubrication and cushioning of valves, is the corrosive action on many seals, diaphragms and sealants. Unleaded fuel was one of the first really successful "green" con tricks of the last Century. Let's not mention combustion products.
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Do you think in a few years time there will be a thread on here asking about running your diesel engined aircraft on chip fat oil?
(excellent posts by pilot dar and jackie)
(excellent posts by pilot dar and jackie)
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It's not really "corrosion" of seals etc. , it's more that they absorb some of the alcohol, and swell up. This often results in their breaking down and leaking, or swelling so as to block fuel flow. Agreed though, that they can be negatively affected. In the case of "O" rings, it is possible to replace the affected ones with tolerant ones, but of course, you'd need an approval! Some alcohols can promote corrosion in aluminum.
The tetra ethyl lead, which is deliberately added to some (much less now) gasoline, is very toxic. As many engines do not require it's properties at all, removing this toxic element is a good thing environmentally. When it was done, it amounted to tens of thousands of tons per year, and that's got to be a good thing to keep out of the air. There are differing thoughts on the need to have it in the fuel for exhaust valves, but consider this: It is very expensive to add, and never added needlessly. The standard permitted it in 80/87, but did not require it, so it was presumably never added. The standard permitted it so as not to disqualify 80/87 which might have been transported in tankers etc. which had carried 100/130, where it would pick up trace amounts of lead. So for all of those decades, those of us who flew on 80/87 only, were running engines as the manufacturer recommended, and with only trace amounts of lead. They did not seem to suffer from it. I am of the opinion that for at least some smaller engines, lead is not requried for valve life. more than 2000 hours of operation of my O-200 on Mogas with no valve seat problems would seem to support this.
Cheers, Pilot DAR
The tetra ethyl lead, which is deliberately added to some (much less now) gasoline, is very toxic. As many engines do not require it's properties at all, removing this toxic element is a good thing environmentally. When it was done, it amounted to tens of thousands of tons per year, and that's got to be a good thing to keep out of the air. There are differing thoughts on the need to have it in the fuel for exhaust valves, but consider this: It is very expensive to add, and never added needlessly. The standard permitted it in 80/87, but did not require it, so it was presumably never added. The standard permitted it so as not to disqualify 80/87 which might have been transported in tankers etc. which had carried 100/130, where it would pick up trace amounts of lead. So for all of those decades, those of us who flew on 80/87 only, were running engines as the manufacturer recommended, and with only trace amounts of lead. They did not seem to suffer from it. I am of the opinion that for at least some smaller engines, lead is not requried for valve life. more than 2000 hours of operation of my O-200 on Mogas with no valve seat problems would seem to support this.
Cheers, Pilot DAR