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Automotive Guide Diesel or Gas - Loud Smoking Dinosaur or Fuel Gulping Monster

By: Simon Byholm
Automotive Guide

In this article I'm going to discuss the properties of the diesel and gas engines, and compare them to each other. I'm specifically referring to their use in automobiles.

Looking at them from a distance both the gas and the diesel engine 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 we look at the engines a little closer that we start to notice that there are differences. Differences in gas mileage, smell, vibrations, price and expected age to name a few.

The gas engine has an ignition system with high voltages, 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.

Another thing that separates the diesel from the gas engine is that gas engines adds the fuel vapor to the air in the intake manifold either through a carburetor or through fuel injection nozzles. The air/fuel mixture is then sucked into the cylinder to be burnt the next time the piston strikes.

The diesel on the other hand sucks clean air into the cylinder and then waits for the piston to compress the air as much as it will go. 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 differences is fuel injection and ignition results in the diesel burning the fuel more efficiently than the gas engine. That's why a diesel has a better gas mileage than it's gas powered counterpart.

This is not to say that a diesel is better. It's different, it has drawbacks too. Diesel engines usually is harder to start in cold and freezing weather. If you remember it was compressed hot air that ignited the fuel. When it's too cold outside the air will never become hot enough to ignite the fuel, and the engine won't run.

To handle this diesels have something called glow plugs for handling cold start situations. Electrical power from the accumulator is used to preheat the glow plugs inside the cylinders before the engine is started. 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 nuisances of having a diesel in your 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 ready or the car won't start. On the other hand if the engine is well done the glowing does not take long and you soon get accustomed to it.

Lets for a second look at the practical differences between the diesel and the gas 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. It also has a sturdier construction due to the higher pressures it must handle and thus can often go twice as many miles as a gas engine during it's lifetime. The sturdier construction also makes it more expensive when first bought.

Features of The Gas Engine

More quiet that the diesel

Better acceleration and higher top speed

Uses an Ignition System with Spark Plugs to Light The Fuel

Adds fuel to the air before letting it into the cylinder

Not as sturdy as a diesel. Lower price but breaks down faster

Gas readily available everywhere

Features of The Diesel Engine

Loud noise, sounds like a truck or agricultural machine

Slow acceleration (get one with turbo charger, that helps)

Lower top speeds but can easily reach the legal speed limit in most places

Uses glow plugs to help the fuel ignite when the engine is cold

Lets clean air into the cylinder and injects the fuel later

Engine is simple and robust. Higher price but runs many miles

Emits black smoke when loading it (like a quick acceleration)

Easy to convert to using Eco fuel oils

If I where to give you advice on selecting either a gas or a diesel powered car I would probably tell you this: Get a diesel if you drive long trips and can live with the small nuisances of more noise and poor acceleration, get a gas powered car if you drive less than average or if you just want the comfort at any price.

Simon Byholm is a software engineer living in Finland. He has a B.Sc degree in electrical engineering and in his free time he makes informative and helpful sites on the Internet. Simon is the owner of http://www.MilesGallon.com, a site helping people improve their gas mileage.

Automotive Guide Tag : Diesel Gas Fuel

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