In this article I’m comparing the diesel and the gas engine and discuss their differences. I’m specifically referring to their use in automobiles.
From a distance the gas and the diesel engines seem to do their work in about the same way. A fuel made from refined crude oil is burned inside a cylinder and the hot expanding gasses forces the piston to move. The movement of the piston is then transferred to the wheels through crankshaft, gearbox and transmission.
It’s when you look closer at the two engines that you start to see the differences. Differences in gas mileage, smell, vibrations, price and expected age to name a few.
With a gas engine there is an ignition system that uses high voltage electricity with wiring and spark plugs. The diesel does not need this, it compresses the fuel/air mixture until it’s so hot it ignites all by itself. In the gas engine it’s the spark plug that ignites the fuel-air mixture through a high voltage spark at the right time.
Also separating the diesel and gas engines is the fact that gas engines mix the fuel vapor with air in the intake manfold before it’s entering the cylinder. The air/fuel mixture is then sucked into the cylinder and is burned the next time the piston passes the compression stage.
On the other hand the diesel engine sucks fresh air into the cylinder and lets the piston compress it to maximum pressure. At this time when the air is compressed and hot enough to ignite the fuel, diesel is injected directly into the cylinder (or a small space connected to the cylinder) through high pressure nozzles. The fuel ignites instantly due to the high temperature in the cylinder.
The different fuel injection and combustion makes the diesel burn fuel more efficiently than a gas engine. That’s why a diesel has a better gas mileage than it’s gas powered counterpart.
I’m not saying that a diesel engine is better. It’s different, it has drawbacks too. A diesel engine is usually more difficult to start in cold, and especially in freezing weather. As you may remember it was the hot compressed air that ignited the fuel. If it’s cold enough outside the air will not become hot enough and it will not ignite the fuel, then the engine will not start.
To handle this diesels have something called glow plugs for handling cold start situations. Electricity from the accumulator heats the glow plugs inside the cylinders before you even try to start the engne. This way the hot glow plugs ignite the fuel when the air is not hot enough to do it. Then when the engine starts it only takes a few seconds for the cylinders to get hot enough to ignite the fuel without help and the glow plugs are not needed again until the next cold start.
This is one of the things that might bother you when having a diesel engine in the car. The glowing takes from a couple of second to half a minute and can easily lead to stress when in a hurry. You just have to wait until it’s done or the car won’t start. On a modern engine the glowing does not take long, it might not even be required, and you’ll soon get accustomed to it.
Lets look at the practical differences between the gas engine and the diesel engine. The diesel is large and loud, it emits black smoke when accelerating and is generally regarded as bad smelling by those not owning one. In addition it has a more robust construction because of the high compression is must handle and can usually go twice as many miles as the same size gas engine during it’s life. The sturdy contruction also makes it expensive when bought new.
Features of The Gas Engine
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