In this article I’m going to discuss the properties of the diesel and gas engines, and compare them to each other. Specifically their usage in cars.

Looking at them from a distance both the gas and the diesel engine work in about the same way. Fuel manufactured from refined crude burns in the cylinder forcing the piston to move from the resulting pressure. 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. 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 a gas engine the spark plug ignites the fuel/air mixture by sending a high voltage spark into it 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 diesels have better fuel economy than it’s gas burning relatives.

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. 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. A couple of seconds after the engine has started it is usually hot enough to ignite the fuel without the help of the glow plugs and these are not used again until the next cold start.

This is one of the nuisances of having a diesel in your 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 more expensive 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 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 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
• MPG is low compared to a diesel

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)
• Top speed is nothing to brag about but there should be no problem maintaining the 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. High price tag but can run many miles
• Emits black smoke when loading it (like a quick acceleration)
• Can be converted to run on Eco fuel oils
• Has a great gas mileage

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.