How does a turbocharger work in a diesel engine?

Question

I know enough about mechanics and how engines work. I know how turbos work in gasoline engines, the fuel/air charge is in the cylinder and the turbo forces in more air and thus more fuel. But if a diesel engine introduces only air and compresses it until the last second when diesel fuel is injected at the top of piston travel, how does a turbo work on a diesel if the fuel isn't present until detonation?

Answer 1

First, a diesel engine introduces fuel into an engine just as a gasoline engine does. The only thing different in the strokes is instead of a spark plug in gasoline engine, deisels just squish it until it bangs. A turbo in a diesel works off the same principle as a car, only bigger and faster. A turbo does NOT give any more fuel, all a turbo does is take the exhaust gas pressure, which spins a turbine, and spins another turbine to increase pressure in the manifold, and hence, push more air into the cylinders during the intake stroke. A diesel needs an immensely more amount of air than a gas engine because of design, so a turbo helps a lot. It's also fun to hear the "whine" it has when it kicks in, and see people look up at you funny. so, basically, here's how it boils down:

Intake - Piston goes down and sucks air into the cylinder. Here's where the turbo forces in more air.

Compression - Piston forced upward by crankshaft, at some degrees BTDC (Before Top Dead Center), fuel is injected in a specific pattern for proper burn pattern, at a few degrees btdc, the cylinder fires. Usually <10 degrees btdc.

Power - Piston reaches TDC and starts the downward stroke, the pressure caused by combustion forces it down, thus creating power.

Exhaust - Piston rises again and forces out the exhaust gases which drive the turbo to create more pressure.

It is important to note here that diesel throttle controls are not like a gasoline engine control. Gas usually controls air flow. A diesel controls the fuel flow into the cylinders. This is because in a tractor trailer, if you were to try to stop the air intake, it would damage whatever you used within minutes because the suction is so strong. There used to be a Detroit V-Block series diesel that was 2 cycle, and had a tendency of actually running backwards, off it's own engine oil, and screwing up everything if the driver didn't get the truck in gear and shut down within an extremely shot time.

Answer 2

A two stroke style diesel engine, the most popular out there today, requires some type of boost source to run like it does. The turbo packs the cylinder full of air when the piston is on the bottom of the stroke and the air is compressed as the piston goes up and diesel is injected in. The diesel engine just wouldn't pull like it does without it. The turbo is not as important on a gasoline four stroke engine, but it sure helps the engine add some muscle.

The turbo works the same way on both engines. The fuel is just introduced into the cylinder in different ways. The turbo does not need fuel to operate.. it just needs a rush of exhaust pressure that exists when the exhaust valve opens.

Answer 3

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RE:
How does a turbocharger work in a diesel engine?
I know enough about mechanics and how engines work. I know how turbos work in gasoline engines, the fuel/air charge is in the cylinder and the turbo forces in more air and thus more fuel. But if a diesel engine introduces only air and compresses it until the last second when diesel fuel is...

Answer 4

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... a naturally aspirated diesel engine works fine on low to medium engine speed since the, volumetric efficiency (how much air enters the combustion chamber) is not greatly affected,, but at high engine speeds, the opening and closing of the intake valves happens so fast that only about half of the air enters the combustion chamber, reducing the combustion pressure,, ... with a turbocharger installed,, more amount of air is forced to the combustion chamber at high engine speeds, thereby creating more combustion pressure, better air fuel mixing thereby producing more power and probably lesser fuel consumption due to better air fuel mixing,,, ... but installing a turbocharger on a natural aspirated engine might require some modifications, the engine will need a new intake and exhaust manifold, probably the camshaft might be replaced or retimed, might also need new oil lines and water hoses for cooling the turbocharger,,

Answer 5

I think you are confusing a turbo with a supercharger. A supercharger is a turbine that compresses air before it reaches the engine.

A turbo charger uses exhuast gases to spin a turbine which in turn is used to pull fresh air in. Something like that anyway. Try www.howstuffworks.com and they can explain way better than I can. A turbo in a diesel would work the same as a turbo in a gas engine.

I'd also like to add that my turbodiesel VW Jetta works great and gets 50 MPG.

Answer 6

How A Turbo Works

Answer 7

its the same as a petrol engine,it packs more air in.effectivly raising the compression ratio