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I think, it could lead to, for example, very environment friendly and very efficient urban traffic.

But I also think, it required very precise part construction.

Do such things exist? At least in plan?

Extension: Clarification added, waiting for acceptable answer again.

Extension #2: Despite the "common sense", diesel engines aren't so simple. Although there is no spark, there is a part which injects the fuel in exactly the perfect moment into the piston. This happens with around 2000atm pressure. Maybe this would be hard in case of gases.

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  • $\begingroup$ Can you clarify what you mean by "diesel-like"? There are multiple things that differentiate diesel engines from gasoline engines, some of them may exist in specific gas engines, others may not. $\endgroup$ – Trevor Archibald Mar 18 '15 at 14:31
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    $\begingroup$ Furthermore -- are you talking purely about reciprocating engines? Gas turbines are also compression-ignition, but can run on, well, just about anything that burns when outfitted with appropriate controls... $\endgroup$ – ThreePhaseEel Mar 19 '15 at 1:11
  • $\begingroup$ Yes, on "diesel-like" I understood compression-ignition - thank you the community the perfect decoding. :-) $\endgroup$ – peterh says reinstate Monica Sep 26 '15 at 16:32
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It depends on what you mean by "diesel-like". If you mean an engine with compression ignition running on gaseous fuel, then the answer is no. The high autoignition temperature of fuels such as natural gas prohibits sparkless ignition of pure natural gas1. @mart is right that compression ignition engines running on gaseous fuels need a pilot fuel which ignites the mixture.

However, diesel engines have been modified to run on gaseous fuels by adding spark ignition2. These engines are "diesel-like" in that they have high compression ratios (and were made from actual diesel engines for purposes of research convenience) so again, it depends on what you mean by "diesel-like".

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  • $\begingroup$ "Diesel-like" means ignition by compression (and thus, very good efficiency). $\endgroup$ – peterh says reinstate Monica Jan 21 '16 at 22:27
  • $\begingroup$ Actually, @peterh, compression ignition (the Diesel cycle) is less efficient than spark ignition (the Otto cycle) for equal compression ratios. It is only because diesel fuel allows for higher compression ratios that it is more efficient. $\endgroup$ – regdoug Jan 23 '16 at 21:39
  • $\begingroup$ Thank you the information, although it is really surprising to me. I think, it is enough surprising for a detailed question & answer. $\endgroup$ – peterh says reinstate Monica Jan 23 '16 at 22:01
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The only ones I know of are pilot-oil gas motors. The ones I know burn biogas or methane plus a small amount of oil, typically rape oil. The oil is neccesary for combustion but the biggest part of the power comes from the gasous fuel. Typically, the lower limit for oil consumption is about 5% (by energy content), the engines can run on oil solely. Efficencies are advertised as 45-50% for a 500kW stationary engine used as a CHP plant (with utilization of exhaust pressure). This is better than gas-only engines. One producer is Schnell Motoren, maybe you can find further information on their site.

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    $\begingroup$ Bristol's Bio-Bus seems to have a diesel engine fuelled by methane $\endgroup$ – dcorking Mar 18 '15 at 11:59
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    $\begingroup$ Diesel engines are more easily converted to biogas combustion. Many Biogas CHPs have retrofitted MAN truck motors as their heart. But thermodynamically these motors have an Otto process, like in a non-Diesel car engine. I assume the buses use an Otto process also. Gas does not ignite easily enough for a 'proper' Diesel process. $\endgroup$ – mart Mar 19 '15 at 14:21
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    $\begingroup$ Do you mean this? Otto cycle versus Diesel cycle In other words, no spark plug, but the igniting high boiling point oil provides the thermodynamic equivalent of a spark, perhaps? Is gas injected in the induction stroke, and oil in the compression stroke? $\endgroup$ – dcorking Mar 19 '15 at 14:27
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    $\begingroup$ I meant those two processes, yes. I'm not sure I understand your question. In pilot oil engines, the oil is injected near the end of the compression stroke while the air and the gas have been compressed. The igniting oil provides the spark, yes. $\endgroup$ – mart Mar 19 '15 at 20:20
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On this website, Wartsila states it has made diesel-gas engines and that the first ones have been operating for 70 000 hours.

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    $\begingroup$ -1 for now: No explanation for in what regards the engines are diesel like. $\endgroup$ – mart Sep 18 '15 at 12:54
  • $\begingroup$ I've googled for it and found meaningful links. It is an engine manufacturer. But there is no sign that their engines would use gas. $\endgroup$ – peterh says reinstate Monica Jan 21 '16 at 22:29
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    $\begingroup$ Well, this should go into the body of the answer: These are pilot oil engines on a diesel cycle. $\endgroup$ – mart Jan 23 '16 at 20:58
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If you count gasoline as "gas", many car manufacturers are already testing homogeneous charge compression ignition engines. It is where they use the compression stroke to ignite the fuel mixture in the cylinder. The fuel is not direct injected, it is premixed in the intake charge before it makes it into the cylinder, so diesel type direct injectors are not necessary.

The same technology could be used for other gaseous fuels such as compressed natural gas. Such as the experimental compression ignition natural gas engine made by toyota, referenced here http://papers.sae.org/2007-01-0176/

So such things do exist, though uncommon.

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  • $\begingroup$ No, gasoline is not gas, it is a fluid. Gases are: methane, ethane, etc. $\endgroup$ – peterh says reinstate Monica Jan 22 '16 at 15:22
  • $\begingroup$ Updated my answer with a mention of toyota's compression ignition HCCI natural gas engine. $\endgroup$ – Netduke Jan 22 '16 at 18:31

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