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 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 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.
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.
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 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. 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. 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. 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. 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 higher quality 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 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 heavy duty contruction 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
- 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. Costs more but will 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 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.
