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cool diesel engine air, cool fuel?

Discussion in 'Technical Discussion' started by Capt Ralph, Dec 3, 2015.

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  1. Capt Ralph, Dec 3, 2015
    #1
    Capt Ralph

    Capt Ralph Senior Member

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    I was typing aweigh on an other thread and some ideas came up.
    Inter-cooling / after-cooling was my thoughts;

    I have always been a fan of the theory. That last cooling of the air just before getting pushed into the cylinders.

    I remember juicing up my truck when I was young. Big air box, near snorkel looking contraption I made driving cool air to the carb.
    Also, A tin box under the hood with copper tubing coiled up in it. The local grocery store still sold dry ice and we would pick up a small chunk, place it in the tin box (fuel cooler) and go off roading.
    Not sure if it helped, read it in a drag racing magazine somewhere. We felt cool though.

    Then I read a few years ago, people heating up their diesel to make it last longer, expansion and quicker vapor I guess. I don't think that worked.

    Now, just thinking about cool air, how about that cool diesel fuel getting in also.
    Yea, I know the fuel is used to cool the injector on most designs, but the newer common rail stuff should be easy to get cool fuel rite to the injector tip.

    Any engineers out there?
  2. Marmot, Dec 3, 2015
    #2
    Marmot

    Marmot Senior Member

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    There isn't much point in cooling the fuel below the maximum allowed by the engine manufacturer. Diesel engine power output is controlled by the weight of the fuel injected up to the smoke point, the point at which there is no longer enough air to burn the fuel. Beyond that you just convert the excess into black smoke.

    Cooling the air increases power output because increasing air density increases the oxygen content per unit of the charge air. This permits burning more fuel and producing more power before reaching smoke point.

    Cooling the diesel fuel will only mean the injector "rack" has to reach a very slightly lower target (either mechanical position or injection duration) to produce the power required. That means cold fuel can provide the same power with a very slightly lower volume than warm fuel. The engine doesn't know the difference because it delivers fuel based on weight. Low heating value fuel (lower density) requires a higher rack position than higher heating (higher density) value fuel. That is easily shown when burning jet fuel as opposed to #1 or #2 diesel fuel ... less power at the same rack or less maximum power available or less mpg if used in a car.

    If there was a way to inject fuel at cryogenic temperatures (can't because diesel fuel gets solid well before that low a temp could ever be reached) all it would do is increase the ignition delay.
  3. Capt Ralph, Dec 3, 2015
    #3
    Capt Ralph

    Capt Ralph Senior Member

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    I understand and thank you.