Adding 71 liters of gasoline to a diesel engine

Alasdair Anderson:

Denis is wrong when he says that petrol would detonate sooner in the compression cycle as that is not where the problem lies. A petrol engine (spark ignition) uses the spark plug to ignite the fuel/air mixture at the correct part of the cycle, but a diesel engine (compression ignition) has a much higher compression so that the fuel ignites as it is injected. Therefore with the injection being at the correct point in the cycle (probably about 5 degrees before TDC) you will not have pre-ignition. The major problem is likely to be with the fuel injectors and pumps as they are designed for diesel fuel rather than petrol, and diesel has different characteristics.

. . .

Hello, Alasdair. Evidently on this occasion I did not make myself sufficiently clear and was a little too casual in my choice of terms. I should not have used the word "detonate", and I am sorry for the confusion this has caused.


I am well aware, of course, that a diesel engine has no spark plugs and the fuel ignites following injection near TDC. I do maintain that the different combustion characteristics of petrol change the nature of the combustion sequence, and this has an adverse effect as well as the deleterious effect of the non-lubricating qualities of petrol.


Much information on the Internet, particularly from breakdown rescue services, focuses on the lack of lubrication quality of petrol, possibly because it is easier to explain, and of course I do not deny this is a major part of the issue. I have found some further interesting articles, which describe the much-faster rate of combustion of petrol within the cylinder.

http://www.differencebetween.info/difference-between-petrol-engine-and-diesel-engine
https://me-mechanicalengineering.com/comparison-between-petrol-and-diesel-engines/


In the diesel engine most of the combustion takes place in the power stroke as the volume expands, whereas in the petrol engine combustion takes place in a shorter period of time at the top of the stroke. In thermodynamic terms, diesel engines are based around the Diesel cycle and petrol engines around the Otto cycle. A diesel-petrol mixture would have characteristics approaching that of petrol so combustion would take place too rapidly for the design of the diesel engine, especially in view of its slower rotation, causing impacting forces that it is not designed to take.


Thank you for agreeing with me on the point of attempting to drive would cause severe damage. It seems that the Land Cruiser described was a tough old beast, and it is amazing it managed 14 km! ?

Alasdair Anderson:

Denis is wrong when he says that petrol would detonate sooner in the compression cycle as that is not where the problem lies. A petrol engine (spark ignition) uses the spark plug to ignite the fuel/air mixture at the correct part of the cycle, but a diesel engine (compression ignition) has a much higher compression so that the fuel ignites as it is injected. Therefore with the injection being at the correct point in the cycle (probably about 5 degrees before TDC) you will not have pre-ignition. The major problem is likely to be with the fuel injectors and pumps as they are designed for diesel fuel rather than petrol, and diesel has different characteristics.

. . .

Hello, Alasdair. Evidently on this occasion I did not make myself sufficiently clear and was a little too casual in my choice of terms. I should not have used the word "detonate", and I am sorry for the confusion this has caused.


I am well aware, of course, that a diesel engine has no spark plugs and the fuel ignites following injection near TDC. I do maintain that the different combustion characteristics of petrol change the nature of the combustion sequence, and this has an adverse effect as well as the deleterious effect of the non-lubricating qualities of petrol.


Much information on the Internet, particularly from breakdown rescue services, focuses on the lack of lubrication quality of petrol, possibly because it is easier to explain, and of course I do not deny this is a major part of the issue. I have found some further interesting articles, which describe the much-faster rate of combustion of petrol within the cylinder.

http://www.differencebetween.info/difference-between-petrol-engine-and-diesel-engine
https://me-mechanicalengineering.com/comparison-between-petrol-and-diesel-engines/


In the diesel engine most of the combustion takes place in the power stroke as the volume expands, whereas in the petrol engine combustion takes place in a shorter period of time at the top of the stroke. In thermodynamic terms, diesel engines are based around the Diesel cycle and petrol engines around the Otto cycle. A diesel-petrol mixture would have characteristics approaching that of petrol so combustion would take place too rapidly for the design of the diesel engine, especially in view of its slower rotation, causing impacting forces that it is not designed to take.


Thank you for agreeing with me on the point of attempting to drive would cause severe damage. It seems that the Land Cruiser described was a tough old beast, and it is amazing it managed 14 km! ?