gasoline direct injection compression ignition engine
gasoline direct injection compression ignition engine
(OP)
Hello, sorry if this question is dumb, but why it is difficult to use petrol in engine which is like diesel? What if petrol would be injected into hot air near tdc using high pressure fuel pump and direct injection, also higer cr engine, like in diesel engines? I saw, that few years ago, Hyundai and Delphi was working on project like this.





RE: gasoline direct injection compression ignition engine
dieselfuel will start to burn more evenly once the auto-ignition temperature is reached - and the auto-ignition temperature is substantially lower, due to the chemical structure of the components that make up the dieselfuel (relatively long and straight hydrocarbons compared with relatively short predominantly branched hydrocarbons for gasoline).
RE: gasoline direct injection compression ignition engine
RE: gasoline direct injection compression ignition engine
Cheers
Greg Locock
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RE: gasoline direct injection compression ignition engine
Diesel fuel is designed to ignite easily with minimal delay when squirted into hot air. Gasoline is designed NOT to ignite easily (i.e. have a rather long ignition delay) when compressed in hot air (that's called "detonation", and it breaks stuff) but ignite easily with a spark (it vaporises much more easily than diesel fuel does). So, if you squirt gasoline into the injection system of a diesel engine ... it either doesn't work at all, or it kindasorta works under some conditions but the engine is quite obviously not happy about it.
Mazda's upcoming "Skyactiv X" engine is worthy of study. It's using premixed air and fuel charge with a lot of EGR ... and spark ignition to light off the charge. The balance of the charge basically detonates intentionally.
So with that, what's your question?
RE: gasoline direct injection compression ignition engine
RE: gasoline direct injection compression ignition engine
RE: gasoline direct injection compression ignition engine
BP - petrol does indeed "workie" in a diesel car (note this in the video) - in fact it probably "workies" a bit better than diesel fuel does. But it will certainly bugger the injector pump etc. fairly quickly. It is common practice in the Australian bush to tip a bit of petrol directly into the intake of a diesel engine if it is reluctant to start.
RE: gasoline direct injection compression ignition engine
RE: gasoline direct injection compression ignition engine
If I remember the Detroit multifuel engine was a 21:1 compression ratio. A small amount of oil can be added like for a 2 stroke chainsaw engine to gasoline for more lubricity. But then how many electronic and now electronic direct gasoline injection systems are in operation? And in the old days how many mechanical gasoline injection systems were used in large aircraft engines, and some higher end cars? Mercedes had an engine that used mechanical injection back in the day.
So yes a diesel will burn gasoline just fine with the correct modifications, a low cr emissions designed one will not do so good.
RE: gasoline direct injection compression ignition engine
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RE: gasoline direct injection compression ignition engine
I believe "since the self ignition quality's of diesel vs gasoline are inverse, meaning diesel is easy to ignite under compression pressure / heat, gasoline is not, octane resists that sort of combustion, so then higher pressures are needed" is incorrect. High and low octain fuels both begin combustion at roughly similar pressures and temperatures. The key factor, as BrianPeterson notes, is ignition delay.
The characteristics of heptane (0 octane) and iso-octane (100 octane) under Homogeneous Charge Compression Ignition (HCCI) are shown below (note HCCI is not the same as the diesel or spark ignition process but often uses one or the other fuel). Diesel #2 is around PRF 62 while most gasoline is near PRF90. The figure shows similar pressures and temperatures for a given ignition point, but significantly different ignition delay.
This figure from the same paper provides more insight into what's happening during compression ignition. Note that all the reference fuels begin ignition near 810K and pass through a period of low temperature heat release then, at around 1100K, begin high temperature heat release when pressure begins a steep climb. After this point, the pressure slopes of the different fuels are similar.
From the figures, it's clear why spark ignition engines use high octane while diesel engines use low octane fuel; spark ignition engines using gasoline exploit the increased ignition delay of high octane fuels to allow more compression before high temperature heat release while diesel engines use low octane so bulk heat release occurs rapidly upon injection of fuel into the pre-heated air.
P.S. Note time-zero associated with ignition delay in the top figure begins when piston acceleration changes sign. This trigger was selected purely for convenience and reflects behavior of the mechanical apparatus used. Per the paper, the time from change of piston acceleration sign to combustion is 0.4 ms, so ignition delays of the figures should be reduced by that time period to remove that bias.
RE: gasoline direct injection compression ignition engine
1 millisecond of ignition delay at 3000 rpm is 18 crank degrees. It's pretty plausible for n-heptane to self-ignite within that time period so it's pretty likely that a compression-ignition engine would run fine on that. But 10 milliseconds of ignition delay for iso-octane is 180 crank degrees at 3000 rpm ... misfire.
"But the diesel engine in the youtube video kept running when they put gasoline in it" ...
Keep in mind ...
They didn't purge the entire fuel system of diesel. They were only trying to simulate someone accidentally putting gasoline into the tank - also not purging the entire fuel system. In the combustion chamber, the remaining proportion of heavier-molecule diesel in the fuel mixture would help light off the gasoline.
They did it with the engine hot. They never showed us a cold-start attempt.
That was an older car ... not one with high-tech common-rail injection. The old prechamber diesels were more tolerant of off-spec fuel.
RE: gasoline direct injection compression ignition engine
You really need to study what high octane rating in a gasoline engine is for and what it does, that validates what I said.