Diesel or Gas – Compares Diesel and Gas Engines
In this article I’m going to discuss the properties of the diesel and gas engines, and compare them to each other. Specifically their usage in autos.
Looking at them from a distance both the gas and the diesel engine 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.
The gas engine has an ignition system with high voltages, 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 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 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 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.
This is not to say that a diesel 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. 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. 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. 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 completed 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. 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 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
Features of The Diesel Engine
- Loud noise, may sound like a truck or agricultural machine
- Slow acceleration (get one with turbo charger, that helps)
- Lower top speeds but can easily reach the legal speed limit in most places
- Uses glow plugs to help the fuel ignite when the engine is cold
- Lets clean air into the cylinders and injects fuel later
- 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 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.
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