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.

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 motion 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.

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 lets the diesel work more efficiently than a gasoline burner. That’s why diesels have better fuel efficiency than it’s gas burning relatives.

I’m not saying that a diesel engine is better. It’s just different, it has it’s drawbacks too. A diesel engine is usually slow to start in cold, and especially in freezing weather. If you remember it was compressed hot 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.

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. 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 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 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 look at the practical differences between the gas engine and the diesel engine. The diesel engine is large and loud and it produces clouds of black strinking smoke when accelerating. 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 robust construction also makes it expensive when bought new.

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

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)
• Lower top speed but can easily reach the legal speed limit in most places
• Glow plugs helps ignite the fuel when the engine is really cold
• Lets clean air into the cylinder and injects the fuel oil later
• Engine is simple and robust. Costs more but will run many miles
• Emits black smoke when loading it (like a quick acceleration)
• Easy to convert to using Eco fuel oils
• Has a great fuel economy

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.