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.
Basic Diesel Quiz.
- What ignites a diesel engine?
- spark plug.
- magneto.
- compression.
- injector.
- Who is credited with inventing the diesel engine?
- Rudolf Diesel.
- ClessieCummins.
- Benjamin Holt.
- Robert Bosch.
- Which fuel has the highest BTU?
- gasoline.
- JP5 jet fuel.
- diesel#1
- diesel#2
- Bacteria growth in the fuel system is a result of what?
- gas in the fuel system.
- water in the fuel system.
- air in the fuel system.
- too much either used on start ups.
- The first diesels were designed to run on what type of fuel source?
- whale fat.
- Coleman lantern fuel.
- coal dust.
- engine oil.
- The first successful diesel engine was built in what year?
- 1914.
- 1814.
- 1905.
- 1895.
- Which one of these things will happen to your diesel engine if you mix a small amount of gasoline in the fuel tank?
- possible explosion.
- poor lubrication.
- knocking.
- all of the above.
- Who is credited with inventing the first diesel fuel pump?
- Robert Bosch.
- Frank Napa.
- VernonRoosa.
- Harley Davidson.
- White smoke on start up is caused from what?
- water vapor in the fuel lines after the injector pump.
- lack of fuel in the injectors.
- water in the exhaust system from condensation.
- lack of heat in the combustion chamber.
- Most diesels have a pump called a lift pump or transfer pump in the fuel system. What do these pumps do?
- provide fuel to the injectors.
- cool the fuel system.
- return fuel to the tank.
- provide fuel to the injection pump.
answers. c,a,d,b,c,d,d,a,d,d
- A diesel engine operates as a?
- 2 stroke.
- 4 stroke.
- Both A&B.
- 8 stroke.
- On amulticylinder diesel 4 cycle engine, all cylinders complete their cycle in ____ revolutions of the crankshaft?
- 1.
- 2.
- 3.
- 4.
- On a 4 cylinder, 4 stroke diesel, the crankshaft interval betweenpowerstrokes is?
- 90 deg.
- 180 deg.
- 295.5 deg.
- 45 deg.
- On a 4 stroke diesel, the intake valve?
- begins to open before TDC.
- closes before BDC.
- closes after BDC.
- both A&C.
- On a 4 stroke diesel, injection of fuel begins?
- on the exhaust stroke.
- on the compression stroke.
- a few degrees before TDC.
- both B&C.
- Valve overlap is?
- when both intake and exhaust are barely open.
- both intake and exhaust are closed.
- occurs at BDC.
- both A&C.
- On a 4 stroke diesel, the exhaust valve closes?
- before TDC.
- after BDC.
- after TDC.
- both A&C.
- A naturally aspirated engine?
- has no turbo.
- has 1 supercharger per cylinder.
- works best at high altitudes.
- gets better fuel economy than a turbocharged engine.
- Propane laced intake air on a diesel will?
- burn hotter.
- burn cleaner.
- burn longer.
- all of the above.
- A naturally aspirated engine has a lower compression ratio than a turbocharged engine.
- true.
- false.
answers: c,d,b,d,d,a,c,a,d,b.
