Diesel or Gas - Who wins The Comparison?

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. Difference in fuel economy, smell, vibration, expected age and price just to name a few.

The gas engine has an ignition system with high voltages, wiring and spark plugs. This is not needed in a diesel as it compresses the air n the cylinder until it's hot enough to ignite the fuel when injected. 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 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. Fully compressed the air is hot enough to ignite disesel and at that point high pressure nozzles will start to spray fuel into the cylinder. 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. A diesel engine is usually more difficult to start in cold, and especially in 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. That way the fuel is ignited by the hot glow plugs while the cylinder and air is still too cold 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. Glowing can take from a couple of second to half a minute and can be quite a stress if in a hurry. You just have to wait until it's ready or the car won't start. On a better engine the glowing does not take long, it might not even be required, and you'll soon get accustomed to it.

Lets for a second look at the practical differences between the diesel and the gas engine. The diesel engine is large and loud and it produces clouds of black strinking smoke when accelerating. 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 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
• Gas Mileage is poor compared to a diesel

Features of The Diesel Engine

• The diesel engine is loud and has the sound of an agricultural machine or an 18 wheeler
• Slow acceleration (get one with turbo charger, that helps)
• Moderate top speeds but can easily reach the legal speed limit in most places
• Glow plugs helps ignite the fuel when the engine is really cold
• Clean air is sucked into the cylinder, then fuel oil is injected
• 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
• Has better MPG than a gas engine

If I where to give you advice on selecting either a gas or a diesel powered car I would 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.