It’s important to understand the pros and cons of diesel and petrol engines and their applications in vehicles. Knowing this will better help us to appreciate these engines and widen our views of which best engine to choose when buying a car for use. Many Nigerians are oblivious to the usefulness of a diesel engine, limiting their knowledge to the norm that only heavy duty vehicles use diesel, but this is wrong. Even some entry level sedan cars use diesel engines for it’s unique advantage over petrol engine.  This will be explained fully below.


Before we proceed let’s look at what happens in both petrol and diesel engines during combustion. Both diesel engines and petrol engines convert fuel into energy through a series of small explosions or combustion. The major difference between diesel and petrol is the way these explosions happen. In a petrol engine, fuel is mixed with air, compressed by pistons and ignited by sparks from spark plugs. In a diesel engine, however, the air is compressed first, and then the fuel is injected. Because air heats up when it’s compressed, the fuel ignites. The video below illustrates this.


Advantages of a Diesel Engine

Engine Longevity: Diesel engines are generally built stronger than petrol engines and tend to last longer. Heavy-duty truck engines will often run up to a 1,609,344 km between overhauls, and diesel cars often go well past 321,869 km with no major engine problems.  This does come at a cost, though, because diesel-powered cars are usually a little more expensive to purchase than gas-powered cars.

Excellent for towing: Diesels produce lots of torque (pulling power) at low engine speeds. For example, a four-cylinder diesel can produce as much torque as a six-cylinder petrol engine. Horsepower ratings for diesels tend to be lower, however, because horsepower is a function of engine speed and diesels have lower maximum speeds than gasoline engines. In other words, they aren’t a good choice for sports cars.

Great fuel economy: Diesel cars can deliver fantastic fuel mileage often approaching that of hybrid cars.  This may be one reason that the Europeans like diesels so much as fuel costs in Europe can be extremely high but this rapidly changing since the cost of diesel is going up.

Can use alternative fuels: Unlike petrol engines, diesels can run on renewable fuels such as biodiesel with no major modifications. Many manufacturers support operation on biodiesel mixes up to BD20 (20% biodiesel/80% petroleum-based diesel) without voiding the manufacturer’s warranty.

Mechanical simplicity: Petrol engines require sophisticated computer-controlled fuel and spark systems to control engine functions. Diesels use a single master fuel pump, and there is no spark system. Look under the hood of a diesel car and you will see a lot less clutter.

Disadvantages of a Diesel Engine

Operating noise: Unlike petrol engines, which produce most of their noise from their easily-muffled exhausts, a good deal of the diesel engine’s noise comes directly from the engine itself. Although manufacturers today are getting pretty good at using sound-deadening insulation in their cars, diesel engines still have a bit of that characteristic diesel clatter.

Initial expense: Diesel engines employ much higher compression ratios than petrol engines. Therefore, they must be built stronger than standard petrol engines. This makes them heavier and a bit more expensive to build.

Engine emissions and maintenance: Though the diesel engine was invented well over a century ago, little attention was paid to emissions until recently. Most modern-day diesel cars rely on diesel exhaust fluid (DEF) an exhaust treatment that reduces the diesel engine’s emissions. These cars have a DEF tank which must be refilled every 15,000 to 30,000 miles per EPA regulations.


Advantages of a Petrol Engine

Petrol cars come cheaper in comparison to diesel version, primarily the reason being that petrol fuel types are manufactured at a lower cost.

Petrol engine cars are responsive, powerful and faster.

Petrol engines are relatively silent in comparison to a diesel variant.

Petrol engines tend to weigh less than the diesel equivalent – an important consideration in a high performance car. Their ‘free revving’ nature also makes them more fun to drive.

Petrol fuel is usually cheaper in comparison to diesel.

Repair cost for petrol engines are typically cheaper than diesel engines.

Disadvantages of a Petrol Engine

Petrol engines are less efficient so use more fuel.

Petrol engines don’t have as much good fuel economy as diesel engines

Petrol engines don’t last as long as diesel engines