Diesel Direct injection - Ford Powerstroke Diesel Forum
 
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post #1 of 5 Old 03-08-2012, 04:55 PM Thread Starter
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Diesel Direct injection

How come diesels have no throttle body but direct injection gas engines do?
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post #2 of 5 Old 03-08-2012, 05:20 PM
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haha, seriously I'm trying to think out a quick and easy response but it's not working.

It basically comes down to the 2 different fuels and 2 different ignition types. Gas engines require a certain stoichiometric ratio to product the optimium amount of power. With no throttle plate you couldn't control the amount of air entering the engine and you wouldn't be able to control the RPMs without starving the engine of fuel and creating a lean hot burn(which will eventually result in a misfire). Diesels however naturally draw in much more air than they need to burn the fuel and don't lean out like gas engines do because of the low volatility of the fuel. Basically you add fuel to add RPMs

You may be better off googling diesel vs gasoline engines. I may not be explaining it totally accurately

edit - and also my grammar sucks when I'm trying to sound smart

Last edited by sinner6.0L; 03-08-2012 at 05:24 PM.
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post #3 of 5 Old 03-08-2012, 05:25 PM
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The short answer is diesel engines do not have throttles. As previously stated, you only control fuel flow in a diesel engine, whereas in a gasser, you have to control both. It all comes down to spark ignition vs. compression ignition.

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post #4 of 5 Old 03-08-2012, 05:26 PM
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Gassers have to maintain air/fuel ratios in a relatively narrow band (IIRC 14.7:1 is optimum). So the throttlebody provides a method to control the amount of air introduced to the combustion process. Diesels do not run the same way, and do not have the narrow air/fuel window

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post #5 of 5 Old 03-09-2012, 06:52 AM Thread Starter
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Quote:
Originally Posted by sinner6.0L View Post
haha, seriously I'm trying to think out a quick and easy response but it's not working.

It basically comes down to the 2 different fuels and 2 different ignition types. Gas engines require a certain stoichiometric ratio to product the optimium amount of power. With no throttle plate you couldn't control the amount of air entering the engine and you wouldn't be able to control the RPMs without starving the engine of fuel and creating a lean hot burn(which will eventually result in a misfire). Diesels however naturally draw in much more air than they need to burn the fuel and don't lean out like gas engines do because of the low volatility of the fuel. Basically you add fuel to add RPMs

You may be better off googling diesel vs gasoline engines. I may not be explaining it totally accurately

edit - and also my grammar sucks when I'm trying to sound smart
This makes sense.
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