Diesel Basics.

A diesel engine is defined by Websters as an engine that ignites fuel by the high compression of air.  There are many dif. between a diesel engine and a gasoline engine.  One thing is, no ignition system to break down.  Fuel is squirted into a combustion chamber, and the heat from compression of air in the cylinder ignites the fuel (diesel fuel ignites at aprox. 450 deg.).

Another thing that differs from gas and diesel engines (not always) is the top of a piston on a diesel forms up the combustion chamber and on a gasoline engine the combustion chamber is in the head.  Like everything else in the world, there are exceptions to this rule.

Here's how a diesel (4 stroke) works.  Fuel flows from a tank to a transfer/lift pump which provides low pressure fuel to the injection pump.  The injection pump transforms this low pressure fuel into extremely high pressure fuel.  This high pressure fuel flows through special high pressure fuel lines to the injectors.  The injector will squirt a fine mist of diesel fuel into the cylinder as the piston comes up on the compression stroke.  This is done before the piston reaches the top or top dead center (TDC).  By the time the fuel is ignited and starts to burn, the piston is now past TDC and is moving back down because of the explosion of fuel in the combustion chamber.  Once the piston is at the bottom of its stroke (BDC), the fuel is completely burnt, and the piston starts to move up again.  This time the cylinder is full of exhaust gas that must be removed.  As the piston goes up, the exhaust valve opens allowing exhaust to escape into the exhaust system.  Once the piston reaches the top of its stroke, the exhaust valve closes and the piston starts to move back down again.  This time the intake valve opens allowing fresh clean air to enter the cylinder.  The piston will move down and "pull" the clean air into the cylinder.  Once it goes all the way down and starts to come back up again, the intake valve will close.  Now the intake and exhaust valves are closed and the piston is pushing this clean air up, compressing it into a small area, the combustion chamber.  This air is extremely hot now that it has been compressed.  As the piston nears the top of its stroke the injector squirts a fine mist of diesel fuel into the combustion chamber and the process starts all over again.  

All of this happens very fast and timing is important.  If you make the fuel enter the cylinder before it needs to, the engine will run very rough, and ignite and burn the fuel before the piston reaches TDC causing the explosion which will try and push the piston down as the piston is trying to come up.  If you try to inject the fuel into the cylinder after its needed the engine will run extremely smooth and will not get the fuel burnt in time before the exhaust valve opens causing the combustion process to continue into the exhaust which will give you extremely high EGT's (Exhaust Gas Temperatures), and will eventually burn the exhaust valve up, not to mention many other things including wearing turbo seals and bearing out do to the  high heat they were not designed to work in.  You also get the entire engine too hot this way, which overheats oil and coolant. 


More to come!

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