Interesting Info on Petrol and Diesel engines

Hi Guys,

I have been thinking of writing a post based on multiple topics, but I have been largely hit by the vast power cuts that have decreased the time I spend in front of computer.

Recently I have been discussing topics related to petrol (gasoline) and diesel engine with my friends. So, I thought of sharing some common questions and answers that may arise.

Please note that this post is not for mechanical or automobile engineering guys. Still, you may find some interesting info here.

1. What is the difference between a petrol and diesel engine?

Basically Petrol engines are spark ignition engines, whereas Diesel engines are Compression Ignition engines.

Petrol engines have carburetors to suck the fuel. The fuel is atomized (or vaporized) and is mixed with air. The air helps the fuel to burn. The air fuel mixture is let inside the cylinder, where it is burned by introducing a spark by means of spark igniter or spark plug. Thus they get the name Spark Ignition or SI engines.

Diesel engines don’t have carburetors, instead they have fuel injectors. Fuel Injectors inject fuel and supply it directly to the cylinder where burning occurs. Diesel Engines don’t have spark plugs. The compression ratio of diesel engine is more and also the auto ignition temperature of diesel is less than that of petrol. So, due to the compression, high pressure and temperature is created which burns the fuel. This is the principle of working of diesel engines and hence they have got the name Compression Ignition or CI engines.

2. Why do motor bikes have petrol engines and not diesel engines?

Some of the older model bikes had diesel engines. Diesel engines are bulky in nature. Carburetors are small, whereas fuel injectors are large and they have to be more accurate for proper functioning. Moreover higher compression ratio means higher vibration. Starting CI engines is quite difficult and particularly it’s hard during cold weather. So, diesel engines are not used in bikes.

3. What happens when diesel is used in petrol engines and vice versa?

Petrol has higher auto ignition temperature and it won’t burn at the compression ratio of a diesel engine without external help. So, the engine won’t run. Whereas when you use diesel in petrol engine, it’s dangerous. Diesel burns with more power and it may damage the engine partly or completely.

4. Why are diesel engine cars more expensive than petrol engine cars? Which is better to buy?

The components of diesel engine are expensive. As said earlier, they have to be manufactured with higher accuracy. Diesel engines have more components compared to petrol engines. This increases the total cost of the vehicle. The taxes imposed on diesel engine cars are also high.

On a long run and continuous usage diesel engine cars end up being cheap. This also depends on a lot of factors like the initial price difference the cars, cost of the fuel (currently petrol prices are increasing, but diesel prices are flat due to the extensive usage), cost of maintenance (diesel engines have higher maintenance costs), mileage, resale value and usage.

Also petrol engine cars are smoother to drive. You may have experienced it earlier. Bikes or petrol engine vehicles have lesser vibration whereas diesel engine vehicles such as buses have more vibration. This is due to the higher compression ratio of diesel engine. Hence the parts will be worn out soon too. With today’s technology the vibration effects are decreasing day by day.

5. Why is petrol red in color, whereas diesel yellowish in color?

Interestingly both the fuels have nearly the same color, except that petrol is dyed red in order to differentiate it from diesel. The color depends on countries, though it is mostly red. In some countries like South Africa, green color is used for unleaded petrol whereas red is used for leaded petrol.

That’s what I remember right now. If you have questions related to this or any other suggestions, please post in the comment section below.

Happy Reading!!!