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 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 transferred to the wheels through the crankshaft, the gearbox and through the transmission.

It’s when we look at the engines a little closer that we start to notice that there are 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. The diesel does not need this, it compresses the fuel/air mixture until it’s so hot it ignites all by itself. In a gas engine the spark plug ignites the fuel/air mixture by sending a high voltage spark into it 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 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 high temperature of the cylinder instantly ignites the fuel.

The different fuel injection and combustion makes the diesel burn fuel more efficiently than a 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. 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.

That’s why diesels have glow plugs that are used when starting a cold engine. 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 the other hand if the engine is well done the glowing does not take long and you 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. 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 sturdy contruction also makes it expensive when bought new.

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. Higher price but runs many miles
• Emits black smoke when loading it (like a quick acceleration)
• Easy to convert for use with 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.