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Diesel or Petrol

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Diesel or Petrol

Old 6th Feb 2017, 15:59
  #141 (permalink)  
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Originally Posted by Peter-RB View Post
I once had a Wolsely 18/85 that could run on for nearly 20 seconds after the ignition was turned off
Time for a decoke . . .
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Old 6th Feb 2017, 22:10
  #142 (permalink)  

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Time for a decoke . . .
You're right.... and derum.
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Old 6th Feb 2017, 22:26
  #143 (permalink)  
 
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I kind of wonder how the Mazda gasoline Diesel cycle engines will avoid the problem that the Mitsubishi GDI (gasoline direct injection) design showed: those are not that far away from Diesel engines in that the fuel has only a minuscule time to mix with the air before it becomes ignited. So they apparently suffer from much heavier soot emissions than a conventionally injected petrol engine.

If the Diesel engine is going the way of the Dodo because of fine particulate matter, nitrous oxides and other nasty things coming out of its exhaust, I do not really see the logic in continuing the basic principle only with a different fuel.

Is there any research done on Stirling engines in vehicles? Continuous combustion, albeit external, surely has its merits compared to multi-stroke engines?
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Old 7th Feb 2017, 02:20
  #144 (permalink)  
 
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The question still is how to stop Pre Detonation and the problem of older cars Running on when switched off....I once had a Wolsely 18/85 that could run on for nearly 20 seconds after the ignition was turned off.
Put foot on clutch, select a high gear, other foot firmly on the brake, slowly release clutch.
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Old 7th Feb 2017, 03:05
  #145 (permalink)  
 
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So they apparently suffer from much heavier soot emissions than a conventionally injected petrol engine.
I believe Toyota have injectors in the inlet manifold to spray petrol on the valves now and again to help clean them. Other manufacturers seem to rely on:

1. Careful combustion design.
2. Not coking up until the warranty has run out, so the owner has to pay for the cleaning.
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Old 7th Feb 2017, 07:23
  #146 (permalink)  

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Originally Posted by MG23 View Post
I believe Toyota have injectors in the inlet manifold to spray petrol on the valves now and again to help clean them. Other manufacturers seem to rely on:

1. Careful combustion design.
2. Not coking up until the warranty has run out, so the owner has to pay for the cleaning.
MG23,
In-port fuel injection is a very common thing these days. The injector sprays the fuel directly onto the back of the inlet valve, which takes heat from it. This cools the valve and provides excellent vaporisation of the fuel, to mutual advantage. Injecting fuel into the manifold is bad for emissions because it can condense on the walls, especially before the engine has reached normal working temperature.
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Old 7th Feb 2017, 07:43
  #147 (permalink)  

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Originally Posted by Peter-RB View Post
The question still is how to stop Pre Detonation and the problem of older cars Running on when switched off....I once had a Wolsely 18/85 that could run on for nearly 20 seconds after the ignition was turned off
Peter, I think you mean "auto (or pre-) ignition". This is normally caused by a flake of carbon in one or more combustion chamber. It glows red hot and works like a continuous spark plug. Because a carburettor will still allow fuel to flow as long as there's a depression in the manifold, the engine will keep running, albeit on one or two cylinders.

Detonation is when the peak pressure caused by the combustion process increases so much that instead of the flame front spreading steadily through the combustion chamber, the fuel air explodes, causing the engine to knock.

Auto ignition can usually be cured by decoking the engine. Some manufacturers, such as Weber, produced carburettors with an idle jet cut-off solenoid, so that when the ignition was turned off, so was the fuel. I've two of these in my garage.
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Old 7th Feb 2017, 13:08
  #148 (permalink)  
 
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ST - I don't think Mazda are going to release a detailed explanation of their new engines combustion processes and controls, because they will be patented and the precise design information will be a "commercial secret".
You can patent an invention, or you can keep it a secret, but you can't do both.
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Old 7th Feb 2017, 13:37
  #149 (permalink)  
 
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In-port fuel injection is a very common thing these days.
Dual injectors aren't common for direct-injection engines. I believe Toyota are the only ones doing it.
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Old 7th Feb 2017, 22:07
  #150 (permalink)  
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I had an 850 Mini which became an unknown capacity Mini after a bore and shaving so much off the head the oil port became exposed. The fix for that was to braze some brake pipe into the trough.

My check of the compression ratio was via a gauge I still have here now. Must be over 50 years old. Anyway, back then it showed 13.2. However, it would only run on 5 Star.

So, <there's that So again. that implies an ability to run if the fuel had been put in at the right time. (Sorry, can't resist it.) A bit of a non-starter really.

Valves would burn out rather before 10k miles, but heck, when it was going it was way better than the Mini Cooper and a bit shy of the 1275S.

The lean burn mode was at 50mph where it would reliably turn out 50mpg. Quite an achievement in the 60's.

Oh, an interesting thing. Honda, if not Toyota, had parts for variable timing gear, and the cams, made in Ipswich, or by the Ipswich based company. That company was a world leader in powdered metals, and the parts, as fragile as eggshells, would be heat-treated until they became phenomenally strong steel. You can see how a complex shape being cast would be a tremendous advantage. The metal shrinks in all directions with near perfect accuracy into the final size. The cams were put on the shafts after manufacture. They wouldn't tell me how they glued those on!
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Old 7th Feb 2017, 22:51
  #151 (permalink)  
 
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Speaking of Toyota. I have owned a number of them and for example my 1996 2.0 GT Celica and my 2002 1.8 Corolla T Sport had cylinder heads made by Yamaha. Their name cast on the end of the block. I believe Toyota used Yamaha for their multivalve technology even on earlier MR 2.

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Old 5th Mar 2017, 08:39
  #152 (permalink)  
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VW Polo as toxic as a fully laden lorry | News | The Times & The Sunday Times

Britain’s leading supermini, the Volkswagen Polo, is among the worst polluters on the road, according to newly revealed test data.

VW, disgraced in the 2015 Dieselgate scandal, pledged then to slash emissions but researchers found that the latest diesel-engined version of the Polo emitted as much toxic nitrogen dioxide (NO2) as a fully laden lorry. “The worst-performing car [in the tests] was a VW Polo with a 1.4-litre turbodiesel engine with NO2 emissions 13 times higher than EU regulations allow,” said James Tate of Leeds University’s Institute for Transport Studies, who analysed the test results. “Its emissions of 1.2 grams of NO2 per kilometre were the same as a fully laden diesel truck with a 13-litre engine that we also tested.”

The tests were commissioned by Transport for London which published the results with a separate paper in an academic journal. In the tests, carried out by Millbrook, a vehicle testing firm in Bedfordshire, a vehicle was driven around London on a predetermined course at night, then again during morning rush hour and for a third time around midday. The pattern of acceleration, cruising and deceleration was recorded and then replicated on a rolling road where emissions could be precisely measured. Then the emissions of 13 cars and four lorries were measured as they followed the same speed profile.

“The key finding was that small diesel cars emitted far more pollution than larger cars and even lorries,” said Tate. Other high polluters included a Vauxhall Astra, Ford Focus and BMW 318d. “On average, the diesel cars tested emitted as much NO2 as 1,000 petrol-hybrid cars. These results also suggest that replacing diesel taxis with petrol-hybrids would be one of the quickest ways to improve city centre air quality,” he said.

One puzzle is why small cars generate more pollution. Tate found they have less sophisticated emissions controls to save money and space. By contrast, the larger VW Passat emerged as the cleanest of all the diesels tested. “This shows the emissions problem can be solved but for cheaper cars the technology is too expensive and there may not be enough space to fit all the extra components,” said Tate......
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Old 5th Mar 2017, 10:01
  #153 (permalink)  
 
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As a diesel owner for the last 20 odd years, this is interesting, but the report doesn't mention the ages of the vehicles tested. If they are brand new, it's certainly a problem.
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Old 5th Mar 2017, 14:28
  #154 (permalink)  
 
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It looks as though the problem with small diesels is that they are just too efficient. By having high temperature combustion (1500deg+), which is necessary for high efficiency, the engine is running hot enough to generate nitrogen dioxide. By making the engine less efficient (with exhaust gas regeneratrion or using a petrol engine instead), this can be avoided, but more fuel, and more carbon dioxide are produced.
Adding a combination of ammonia & urea the the exhaust gases breaks down the nitrogen dioxide, but is an additional expense and process for the vehicle operator.

NOx emissions from diesel engines
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Old 5th Mar 2017, 17:24
  #155 (permalink)  
 
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Could someone give us the facts on how much actual harm was done to health due to the use of leaded petrol compared with the actual harm done to health by the use of diesel? No emotions please, just facts.
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Old 5th Mar 2017, 18:19
  #156 (permalink)  
 
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Originally Posted by Trossie View Post
Could someone give us the facts on how much actual harm was done to health due to the use of leaded petrol compared with the actual harm done to health by the use of diesel? No emotions please, just facts.
How long is it since leaded petrol was used in the UK?
1998 was it?
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Old 5th Mar 2017, 18:22
  #157 (permalink)  
 
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It is alleged that the general reduction in violent crime over the last two decades is due to the removal of lead in petrol. Lead harms the brain in a very serious way, which may lead to unsuitable behaviour in a civilised society.
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Old 5th Mar 2017, 18:40
  #158 (permalink)  
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Originally Posted by Espada III View Post
It is alleged that the general reduction in violent crime over the last two decades is due to the removal of lead in petrol.
And the demise of the house sparrow apparently.
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Old 5th Mar 2017, 19:30
  #159 (permalink)  

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Pesky sparrows... always were violent criminals.

I was able to fill my sports car with leaded 4 Star long after 1998, but only available from a few outlets.

Obviously, AVGAS "LL" still contains more lead than that road fuel ever did.
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Old 5th Mar 2017, 19:34
  #160 (permalink)  
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Leaded 4-star petrol was withdrawn from sale in 2000.
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