• Petrol Engine versus Diesel Engine

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  • TD engine

The endless debate between car fans. It started alliances and ended friendship (I personally know examples from both cases). This topic has been around ever since the car itself. This article is dedicated to the two engines.

First of all, a remark should be made. The diesel engine compared in the following is a four stroke one, as found in production cars.

Each of the four strokes has a different role: inlet, compression, expansion and exhaust. Both of the engines were based on the same physical system, but each works in its own way.

The Inlet Stroke

In the petrol engines, the mixture between air and fuel is drawn in by the falling piston. In the diesel engine. Air alone , without any fuel is drawn by the falling piston

The Compression Stroke

The petrol engine compresses the air-fuel mixture up to about 1/10th of its original size, while the petrol engine compresses only the air up to 1/22nd of its original size

The Expansion Stroke

Here’s where the big difference is. The air and fuel mixture in the petrol engine, is ignited by spark and burns, expanding and forcing the piston down. In the mean time, in the Diesel engine, fuel is injected at a high pressure into the hot, compressed air in the cylinder, which causes it to burn. (No spark is required!)

The Exhaust Stroke

This process is the same for both petrol and diesel engines. The burned mixture between air and fuel is pushed out of the cylinder by the rising piston.


In never ceased to amaze me how all of this process take place one after another, putting the wheels in motion.

Compression Ignition vs Spark Ignition

In the diesel engine, because the air in the Compression segment is so hot and compressed, the fuel injected is burned straight away. This is why the diesel engine can be termed as “Compression Ignition”. A petrol engine ignites with the help of an incandescent spark. Hence the name of “Spark Ignition”. This means no breakers, coil or h.t. leads to go wrong. This makes diesels immune to cold and damp that can affect petrol engines.

Other Differences
    Petrol Engine versus Diesel Engine
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    TD engine
  • A diesel engine is more easily turbocharged than a petrol engine, due to the fact that if the compression ratio and the pressure in the cylinder is to high during the inlet stroke, the mixture starts to burn to soon, while the piston is on its way up. The diesel engine has no fuel in the cylinder, thus letting the turbocharger suck as much air as it can without creating any problems.
  • Electronic engine management not necessary. Some modern diesel engines are gaining electronically controlled injection pumps, but the vast majority of them out there have purely mechanical pumps. If you’re into DIY and don’t trust the electronics found in most cars, then a diesel will be a relief. In fact no electricity is required to make a diesel engine run, except for a simple fuel cut off solenoid so that you can switch the thing off! If your alternator stops working, then you’re gonna get home in a diesel.
  • A diesel engine is going to last longer, due to the fact that petrol destroys lubrication and diesel doesn’t.
  • Engine breaking is tougher in the diesel due to the 22:1 compression ratio. But a petrol engine is more likely to start than a diesel one. You do need a good battery to start the second motor.
  • Petrol engine are lighter, while diesel engines even dough they are heavy they have more torque.
  • A diesel engine makes steering heavy.
  • Petrol cars rev up to 7-8 thousand, while diesel ones go up to 5 thousand.
  • If you take two cars with same cylindrical capacity, one diesel one petrol with same horse power and if we consider that the drivers of both of the cars are experts, 0-60mph and ¼ mile , the petrol fueled one is always going to win.


I own a diesel car.I am pleased of the mileage. I invested lots of cash in it transforming it from 90 horsepower to somewhere between 140 and 150. But if I had the opportunity I would not hesitate to buy a petrol-fueled engine car. But that’s just me…

Caesar Alvarez
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  (1) posted on 09.16.2014

interested in knowing more about how turbo charger work on petrol enging

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