Niagara Gazette

Features

November 28, 2013

TOM'S CORNER: Time for a litte diesel engine 101

Niagara Gazette — Well folks, diesel engines are here to stay. Virtually every carmaker has plans for a diesel engine either in their pickups, SUVs or passenger cars. Its only a short matter of time before we will see diesel pumps added to gas stations that previously did not offer diesel fuel. Now Audi has started a TV ad campaign which shows a young woman filing her Audi diesel powered car at the filling station. Well-meaning fellow motorists are shouting to her things like: “Hey! That’s diesel fuel!” or “Stop it right now before you do harm to your car!” to which she responds basically; “Relax everyone, I know what I’m doing.”

This article is meant as a refresher course to those of you who consider yourselves “Diesel Savvy” and intro to those of you who are new to the diesel power scene. Read on and enjoy.

Major differences between the gasoline engine and the diesel engine are:

IGNITION

Gasoline engines take in a mixture of gas and air, compress it, and then ignite the mixture with a timed electrical spark.

Diesel engines take in only air, compress it to super-heated temperature and then injects fuel into the super-heated compressed air. It is the heat of the compressed air that ignites the fuel spontaneously generating the downward power stroke of the piston.

COMPRESSION RATIO

Gasoline engines compress air/fuel at a ratio of 8:1 to 12:1 (on average)

Diesel engines compress at a ratio of 14:1 (and as high as 25:1). The higher the compression ratio of the diesel engine, the better the combustion and fuel efficiency.

FUEL DELIVERY

Gasoline engines generally use either carburetion (this system pre-mixes the air fuel mixture at the top of the intake manifold, far from the cylinders), direct electronic fuel injection, in which case the air/fuel mixture is injected into a port, before the cylinder at the beginning of the downward travel of the piston on the intake stroke. Finally indirect injection, this is where the fuel injector is located away from the cylinder and the air/fuel mix travels to the cylinder via intake plenums.

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