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The question is asked for various proportions : - 10% of petrol - 50% of petrol - 100% of petrol in a diesel engine.

PS : not a duplicate of What happens if unsuitable oil is used in a vehicle engine? !

If you mention a possible damage, please specify the technical reasons with it.

EDIT : didn't know the petrol equivalent in English. Thanks for the suggestions to edit.

* EDIT * : Please upvote the question. It has -4 downvotes, that are NOT justified.

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Just to clarify: you mean using oil as fuel, right? – bububaba Jul 2 '12 at 9:00
@bububaba: Yes ! – Skippy Fastol Jul 2 '12 at 9:18
It would be really helpful if you edited your question to specify: what type of oil? Vegetable oil? Crude oil? Fry oil? Biodiesel? Offroad Diesel? Gasoline? All these are 'oils'. Also, 'used' is too vague. Used in the crankcase? Fuel? Power steering? Transmission? Lots of things 'use' 'oil'. – Ehryk Jul 2 '12 at 11:24
I am tempted to close as not a real question. It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, and cannot be reasonably answered in its current form. I will leave it open for now but I need you to edit the question and be more specific. – Move More Comments Link To Top Jul 2 '12 at 16:56
@Larry: I will edit the question. What seems incomplete ... ? Just asking what are the implications of adding petrol to gasoil for a gasoil engine, for various addition percentages. It's up to the person who replies to be accurate. – Skippy Fastol Jul 3 '12 at 9:36
up vote 5 down vote accepted

The key differences between petrol and diesel engines is the method of combustion.

Petrol ignites with sparks or with compression. Diesel doesn't ignite so well, but burns much better through compression.

Petrol engines inject the air/fuel mixture and then use spark plugs to ignite the mixture just after a piston reaches top dead centre.

Diesel engines compress air, and then add air/fuel mixture. As a result they run hotter. The compression and heat give combustion, rather than flash ignition.

The differences between the fuels are measured on the octane or cetane rating. Fuels with a high octane have a low cetane and are easy to ignite, so work well in petrol engines. Fuels with low octane and high cetane ignite by combustion so work well in diesel engines.

I've heard that a very small amount of petrol (0.5L in a full tank) can actually improve the efficiency of a car, but this must be treated as a rumour. Engine damage could still occur.

10% petrol will result in "knocking" or "pinking", where the engine runs very rough. This is because the petrol will ignite prematurely in the diesel engine, and there will be a loss of power as the combustion happens over a longer time than with 100% diesel. Some damage may also occur to the fuel supply system as petrol is less lubricative than diesel, and strips out some of the lubrication needed for diesel pumps to work well. Example:

50% petrol will result in engine damage, as the incorrect timing of combustions will put high stresses on engine components. Something like this would happen:

100% petrol will also kill the engine. Think along the lines of these:

Other references

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Amazing answer. Many thanks. – Skippy Fastol Jul 25 '12 at 11:45
Two problems with this answer: 1) High octane fuel does not burn as well as low octane fuel. The property of it not burning as well allows it to work in engines where pre-ignition could become an issue. 2) Petrol in diesel engines doesn't work because the petrol will burn up much faster than diesel, not because it burns up over a longer period of time. The reason diesel fuel works in compression ignition systems is because it burns over a much longer time. It's also the reason why diesel engines cannot spin as high ... the diesel wouldn't have enough time to completely burn. – Pᴀᴜʟsᴛᴇʀ2 Mar 25 '14 at 10:47

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