rlp in Co.
Well-known Member
I have always been fascinated by engines and I know that a lot of you guys are too. I found this link to be interesting.
Fuel injection
Fuel injection
- Thread starter rlp in Co.
- Start date
buickanddeere
Well-known Member
. A DI gasser.The advantages of Diesel engine without the disadvantages of a diesel.
John in Mich
Well-known Member
- Location
- Ypsilanti, Michigan
Wife's 2012 Impala is direct injection. Throaty and quick for a V-6.
used red MN
Well-known Member
- Location
- Coon Rapids, MN
Generally in the auto and truck world comparing a diesel and gas engine of roughly the same size the diesel will
generally get the better fuel mileage. Now I believe they say per a given amount of fuel the diesel fuel has more
useable energy. So taking that into account I have wondered if any research or calculations have been done on
the fact that a gas engine is more often than not working against the pull of vacuum created by its cylinders. So
by that fact doesn?t the Diesel engine internally use less of the hp it is creating? The air being drawn in a diesel
is not being restricted. I believe in the case of a direct injection gas engine it still has to regulate the air entering
the engine to maintain the proper air to fuel ratio for the engine to run optimally. Anyone have thoughts on this?
generally get the better fuel mileage. Now I believe they say per a given amount of fuel the diesel fuel has more
useable energy. So taking that into account I have wondered if any research or calculations have been done on
the fact that a gas engine is more often than not working against the pull of vacuum created by its cylinders. So
by that fact doesn?t the Diesel engine internally use less of the hp it is creating? The air being drawn in a diesel
is not being restricted. I believe in the case of a direct injection gas engine it still has to regulate the air entering
the engine to maintain the proper air to fuel ratio for the engine to run optimally. Anyone have thoughts on this?
Red,
You are correct in your assumptions, a Diesel will always be more efficient due to BTU's per gallon and compression ratio's. The direct injection gasser's are getting closer, as compression is in the mid 12s, but you do not have to deal with the soot a Diesel produces. I do not know if these high compression gas engines produce a lot of NOx, but would assume they do, so maybe DEF is in the works for them.
You are correct in your assumptions, a Diesel will always be more efficient due to BTU's per gallon and compression ratio's. The direct injection gasser's are getting closer, as compression is in the mid 12s, but you do not have to deal with the soot a Diesel produces. I do not know if these high compression gas engines produce a lot of NOx, but would assume they do, so maybe DEF is in the works for them.
Brendon-KS
Well-known Member
- Location
- Goessel, KS
When it comes to NOx emissions the throttled intake of the gasoline engine gives it a big advantage over a diesel. One of the ingredients in the NOx creation recipe is more air in the combustion chamber than what is needed by the combustion process. The throttle can be used to allow only the air needed for the given fueling rate to enter the engine which ensures that the oxygen gets combined with carbon and not with nitrogen.
rlp in Co.
Well-known Member
You are right about the vacuum reducing the efficiency of a gasoline engine over a diesel. They used to have contests where guys would compete to see which car and driver could get the best miles per gallon of gas. This was a long time ago but even with older cars they were getting fantastic mileage!. One of the tricks that they used, was to hold the throttle wide open till they got up to speed and then they would shut the engine off and coast. They would do that over and over. That would let the engine be just as efficient as a diesel except for the higher heat value of the diesel fuel. You could never drive like that on the highways but I thought it was interesting.
To name one brand Toyota is still using port and direction injection on a few engines. They have the capability of using one injection method or the other and also both at the same time. The technology is not used to keep intake tract or valves clean, but that is one of the multiple benefits.
Also an interesting spec of gas direct injection GDI, is the injection pressures are around 3000 psi, that is a lot for gas which has very little lubricating properties for pumps/injectors. BTW, modern common rail diesel engines are around 30,000 psi.
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