Diesel or Gas - Compares Diesel and Gas Engines
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 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. 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. 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 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 mpg 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. 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. 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 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 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. 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.
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
- Loud noise, sounds like a truck or agricultural machine
- Slow acceleration (get one with turbo charger, that helps)
- Lower top speed but can easily reach the legal speed limit in most places
- Uses glow plugs to make the fuel ignite when the engine is cold
- Pumps clean air into the cylinder and injects the fuel 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.
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