Diesel or Gas – What to Choose
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 function 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 lets the diesel work more efficiently than a gasoline burner. That’s why a diesel has a better gas mileage than it’s gas powered counterpart.
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 more difficult 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. 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. 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 modern 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 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
The Diesel Engine
- Loud noise, may sound 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
- 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)
- Can be converted to run on 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.
