In this article I’m comparing the diesel and the gas engine and discuss their differences. Specifically their usage in cars.
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 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. Fully compressed the air is hot enough to ignite disesel and at that point high pressure nozzles will start to spray fuel into the cylinder. 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 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 harder 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. 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 nuisances of having a diesel in your car. Glowing can take from a couple of second to half a minute and can be quite a stress if in a hurry. You just have to wait until it’s ready or the car won’t start. On a more expensive 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 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
- Gas Mileage is poor 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)
- Moderate top speed but can easily reach the legal speed limit in most places
- Have glow plugs to help the fuel ignite when the engine is cold
- Pumps clean air into the cylinders and injects fuel later
- Engine is simple and robust. High price tag but can run many miles
- Emits black smoke when loading it (like a quick acceleration)
- Easy to convert to using 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.