How diesel engines work
By Marshall Brain
http://www.JewishWorldReview.com | (MCT) You may have noticed recently that you are hearing more and more about diesel cars. That makes sense because diesel engines get better gas mileage than gasoline engines. With gas prices rising so much, people are very interested in any technology that cuts the amount of fuel that cars use.
But have you ever wondered why diesel engines get better mileage? By understanding how a diesel engine works, the mileage advantage makes a lot more sense.
Chances are that you own a car, and that your car is powered by a gasoline engine. So let's start with it. Your engine contains pistons that move up and down. When the piston moves down, it sucks in air and gasoline. Then the piston moves up and compresses the air and gasoline. Then the spark plug fires to ignite the gasoline. That produces a lot of heat, which expands the air, pushing the piston down. The expansion is where the power of your engine comes from.
One problem with the gasoline engine is the compression part. A gasoline engine mixes the air and gas together and THEN compresses it. That limits the amount of compression that the engine can use. You can only compress gasoline so far before it spontaneously explodes. Whenever you hear your engine knock, what you are hearing is these spontaneous explosions. Knocking is bad because it damages the engine.
More compression would make the gasoline engine more efficient. And more efficient engines get better mileage. But as you can see, there is a limit to how much compression you can apply in a gasoline engine.
A diesel engine solves the compression problem, and that is one thing that gives it better mileage than a gas engine. In a diesel engine, there is no spark plug. And the engine inhales nothing but air. The diesel engine compresses that air about twice as much as a gasoline engine would. Then the diesel engine injects diesel fuel straight into the compressed air. The air gets so hot from the compression that it ignites the diesel fuel without any need for a spark.
This is a pretty simple change in design, but it can really improve the efficiency of the engine. The best diesel engines might be up 50 percent more efficient than a gasoline engine of the same size.
Diesel engines have one other trick up their sleeves as well. It turns out that diesel fuel is different from gasoline. Both diesel fuel and gasoline are made up of chains of carbon and hydrogen atoms. But in diesel fuel, the chains are longer. What that means is that diesel fuel is actually heavier than gasoline. If you buy one gallon of gasoline and one gallon of diesel fuel, the diesel weighs more. So the gallon of diesel fuel contains more hydrogen and oxygen atoms than the same amount of gasoline. Meaning that there is about 17 percent more energy in a gallon of diesel fuel than there is in a gallon of gas.
When you add the improved efficiency of a diesel engine to the extra energy in diesel fuel, you have an engine that gets much better mileage than a gasoline engine.
Now this does not mean that diesel engines are perfect. For one thing, a diesel engine is heavier than the same gasoline engine because the diesel engine has to handle all of the extra compression pressure. Heavy engines tend to reduce mileage. Diesel engines tend to produce more soot, although this problem seems to be getting much better in the newer designs. And diesel engines prefer to turn slower than gas engines, meaning that a diesel car may not accelerate as fast as a gasoline car.
The thing that may make all of these problems with the diesel go away is the idea of a hybrid car. We all know that gasoline hybrids are efficient. A diesel hybrid could be even better. Because of hybrid technology, we may see the rebirth of the diesel engine, and you may soon have a diesel car in your garage that gets great mileage.
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