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Diesel engine horsepower

  1. Oct 19, 2013 #1
    Hello all;

    I have been thinking about this for some time and searching through the internet for it but couldn't get a satisfactory answer for it, so i decided to ask this to you. Here is my question:

    If diesel fuel has more energy in it than gasoline does and if diesel engines are more efficient than gasoline engines, why do diesel engines create less power? For example, a car with a 1.4 diesel engine cannot exceed 130 km/h on a straight road but a car with gasoline engine with the same properties (except it's a gasoline engine:) ) can go up to 150 km/h. As far as i know, obstacles to speed on a straight road is just the air friction and that means gasoline engines produce more power (P=F.V), don't they?

    Im stuck here and I will appreciate any help from you, thank you for your interest.
  2. jcsd
  3. Oct 19, 2013 #2


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    Gasoline engines tend to run at higher RPMs than diesel engines. For running a car at high speed, an engine turning at high RPM is a necessary condition, assuming sufficient power is available to overcome drag.

    As has been discussed in these forums before, due to the nature of diesel combustion, there is an upper limit to engine RPM beyond which there is insufficient time available for complete combustion of the diesel fuel to occur.

    It's not that diesel engines create less power than gasoline engines, it can be viewed that they create the same power with less fuel. Most diesels are designed for economy of operation, not top end performance.
  4. Oct 19, 2013 #3
    OK, i understand thank you very much.
  5. Oct 19, 2013 #4
  6. May 27, 2015 #5
    Not knowing many of the specifics of your example, I can't really give an explanation regarding it. I can say that, in general, diesel engines DO have more horsepower and torque than a gasoline engine with the same displacement. Drop-for-drop, diesel fuel has much greater potential energy than gasoline. In modern diesel engines, they are considerably efficient due to the use of turbo chargers and intercoolers.
    Noteworthy: the vehicles you are using as your example very likely have a factory-set limit on the revolutions/minute that the engines can output.... and/or the speeds you mentioned just happen to be the mechanical limit of the engine.
  7. May 27, 2015 #6


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    As high speed diesels have evolved their dynamic performance has approached that of gasoline engines.
    Some very significant steps in the evolution so far have been indirect injection, turbo chargers and common rail electronic injection.

    Diesels may have a compression ratio of 20:1 which requires heavier construction than a gasoline fuelled SI engine with a maximum compression ratio closer to 10:1.
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