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.

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 movement of the piston is then

transferred to the wheels through crankshaft, gearbox and

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.

Ignition System

The gas engine has an ignition system with high voltages, 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 fuel ignites instantly due to the high

temperature in the cylinder.

The differences is fuel injection and ignition results in the

diesel burning the fuel more efficiently than the gas engine.

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 different, it

has drawbacks too. Diesel engines usually is harder to start in

cold and 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.

Cold Starting a Diesel

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. 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 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 the other hand if

the engine is well done the glowing does not take long and you

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 sturdier construction also makes it more expensive

when first bought.

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

Features of The Diesel Engine

• Loud noise, sounds 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 cylinder and injects the fuel later

• Engine is simple and robust. Higher price but runs many miles

• Emits black smoke when loading it (like a quick acceleration)

• Easy to convert to using Eco fuel oils

If I where to give you advice on selecting either a gas or a

diesel powered car I would probably 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.