I write a diploma on the topc Otto (avgas) and diesel engines for small aircraft operating base and I need information about this topic. I appeal to men smarter, because you have an opinion or knowledge about this topic. I'd be very grateful if you could post this kind of information to me, because I can not find such information.
Does anyone has any experience flying a plane compression, maybe is/has oprating(ed) a diesel aircraft, so what is its plusses and minuses comparing to similar avgas airplane. (maintenence, flying, installiation compression engine, whats its features etc). If you have not operating/ flying it, maybe you know somebody who has or you know how to get thiskind of information. All posts are welcommed, thanks in advance
It is not post- matura, (finishing secondary scool / wikipedia) I think. I´m studying in collage, s.o. If you think that the complication for diploma is not enaugh... The information is hard to get, because there isn´t no more information on engine manufacters homepage besides engine data. On www.dieselair.com is a newsletter, like "Cessna 172 has new diesel engine mounted or there is a new engine coming up". And, maybe some on you have flown with diesel engine airplanes. I need more info, and more specifically, certain facts about airplanes, then I can put all things together. Besides, I´m doing diploma for my first time and I only asked for little help, if the thread is not in topic then you can put it in lock.
Be careful not to confuse the comparison of a WWII technology engine with a 21st century engine, but really an Otto vs. Diesel comparison ! In principal if you need a light engine which is most efficient close to maximum power and does have its maximum torque close to max power (this is what an aircraft and a propeller requires) then Otto is the clear answer. If you want to have the best absolute efficiency and the highest efficiency at low power levels, including high torque at low speed (this is, what cars and even more trucks require) then Diesel is the answer. Limiting factor for Otto is the speed of the flame which limits the size of the zylinder. This means you can not efficiently produce more than approximately 50 hp per zylinder (uncharged) at a typical propeller speed. So it is either a geared engine or lots of zylinders or supercharging if you want to go beyond 300 hp. For Diesel it is more the speed, than the zylinder size which limits it, which is no problem as propellers need to run 1500-2500 U/min depending on the exact diameter epending on the total power you need. This is about the speed at which an ungeared Diesel is best. As aircraft engines are all about flying, meaning high altitude, turbocharging is almost a must if you do not want to have "high and hot" density issues. Diesel are much easier and much more efficient to turbocharge.
This is an interesting subject, never knew a diesel piston aircraft engine existed. Not to sound like a smartass but all the diesel engines in the sky were jet engines to my knowledge. From what I understand diesel is nothing more than jet-a with oil added for lubrication, more or less kerosene.
I would believe cooling and weight would be issues.
A few years ago a company here in the US marketed a twin Diesel engine powered aircraft. I'll try and find something about it, cannot remember the name of the aircraft or the company.
Also, either the British R101 or R102 airship, can't remember which right now, was powered by Diesel engines, it was the Government designed and built airship that crashed, resulting in loss of many crew members. As far as I know, the Diesel engines had no factor in causing the accident.
An excellent book on this airship design is "Slide Rule" by Nevil Shute (Norway).
Can be run on Jet A (if injection pump can cope with lower lubricity compared to automotive diesel fuel)
Fuel system less susceptable to vapour lock
Max torque occurs at lower rpms
Does not require stoichiometric fuel/air ratio
Usually offers significant reduction in fuel consumption
Fuel does not boil off at altitude
High compression ratio requires stronger and heavier components
Torque reversal at low rpms is damaging to reduction drives and alternators (torsional damper required on reduction drive and sprag clutch on alternator)
Technology for aircraft use is still maturing
The USA, the largest potential market, does not offer big cost savings on the fuel, only on efficiency of operation
Fuel is heavier
Leaks on high pressure fuel pipes a fire risk if near hot surfaces
Four stroke diesels allow engines to be based on automotive units, such as Thielert, Austro Diesel, Peugeot etc.
The French SMA engine is four stroke but does not appear to be based on a car engine.
Two strokes such as the Wilksch WAM125 and Weslake W100, offer more firing cycles per revolution.
The most proven diesel engines in aircraft were the Junkers Jumo 205 and 207 engines used in the Junkers Ju86 Bomber and the Blohm & Voss BV138 flying boat. These were built under licence as the Napier Culverin, which was developed into the Napier Deltic Engine used in minesweepers and locomotives. Napier also made the Nomad compound diesel engine which was intended for the Avro Shackleton but never used in it. The Nomad was for a long time (may still be?) the most fuel efficient aero engine ever built.
Allyn, Thanks for posting the links to the Guiberson diesel. I knew there was a pre-war American diesel radial, but I had never heard of this one. I'm surprised it hasn't found its way into any American experimental aircraft, as there appear to still be fair few around. Google says they were uses in Stuart tanks, landing craft and generator sets.
There is a liquid cooled diesel engine manufacturer in my general area that has been plodding away steadily over the years and is getting close to certifying their engines. DeltaHawk Diesel Engines There are some flying in experimental testbed aircraft. USN is also interested last I heard. Compared to gasoline engines, a very significant improvement in specific fuel consumption.
Thank you for answers. Does anybody know, how about noise, vibration, maintenence? I spoke by e-mail with president and chief operating officer for Finch Aircraft and he said that noise and vibration are heavier and maintenence is costlyer than avgas piston engine. In my opinion, the maintenence should be cheaper, because in diesel engine is less parts to worry about (except cooling issue and gearbox of course). But then again other companies tell otherwise; for example: SMA What do you think?
Rabauss, I suggest you go back to your man at Finch aircraft and ask him to clarify what he means by more expensive. Thielert/Centurion had some components (torsional damper, gearbox, oil nozzle for connecting rod little end) which were upgraded on their 1.7 engine, and due to the company operating in a 'Chapter 11' type bankruptcy state, these upgrades were not covered by warranties as the might otherwise have been. This has been discussed at length over the last couple of years on PPRuNe, so type in Thielert or Diesel in the search function and have a good read.
Vibration may be more at idle RPM, due to the engine's higher compression ratio resulting in more torque reversal. A lot would depend on the design of the engine mount and any anti-vibration mounts used.
I don't see why diesels should be significantly cheaper than a petrol engine to make, although a few parts are still sourced from the automotive industry which would bring prices down with mass production. As there are comparatively few around, the development costs are still being absorbed in the engines being sold, and the parts count is significantly higher with many high performance precision components (such as gearboxes, injection pumps & injectors).
And not to forget, you should compare the torque over speed curve with the propeller curve and have a look at the torque over crankshaft angle curve. The first one demonstrates that a diesel always needs an adjustable (typically meaning constant speed) propeller, while the second one lets you estimate the TBO of your propeller blade bearings... close to zero! That´s why the Thielert needs a torsional damper. Diesels are doing incredible torque peaks at the time of fuel explosion while an otto burns the fuel smoothly. Of course there is a lot you can optimize with electronically controlled high pressure injection, but that adds plenty of complexity, sources for failure, life limited components, maintenance costs etc.
I have been flying the Thielert Diesel engine in a 172 now for five years or so...(first the 1.7 and now the 2. litre engine). If you want to set out any questions about handling please do and I will try to help...or else PM me for the information.
Please bear in mind...I only fly them...I do not have a lot of technical data as others have kindly given you here....but as to flying a Diesel/FADEC engine, I will help if I can.
DERG, Could you please elaborate on what you mean by "fuel freeze"?
My understanding is that with most aero diesel engines running on Jet A1, the fuel would have to get to -47°C to get fuel waxing, and this also seems to be a thing of the past with automotive diesel thanks to modern additives. The bulk of fuel in the tank and the temperature generated by the work done in the injection pump would suggest these stay warm too?
I have heard of intercoolers overcooling under some conditions, but that isn't a fuel issue.
As for fuel cleanliness, why would this be any worse than for any other fuel or engine type? Aircraft, in most cases, operate in a much cleaner environment than earthmoving equipment, off road vehicles, etc. and effective filtration works for them.