Diesel vs Petrol Fuel

With international oil price climbing above 135 US dollars per barrel, prices of fuel is going to go in one direction - UP. Every penny saved is a penny gained for the common man who has to fill at the fuel station. Which vehicle is better suited for you ? - Diesel or Petrol ?

What are the advantages of a diesel car compared with a petrol car ?

Diesel VS Gasoline / Petrol

Advantage of Diesel Technology:

Diesel is derived from petroleum like gasoline is. Its density is 850 gms/liter whilst the density of gasoline is about 15 % less at 720 gms/ liter. It also releases more energy than petrol. Compare this - Diesel puts out about 40.9 MJ (mega joules) per liter while petrol puts out about 34.8 MJ per liter. As a result, diesel engines are far more fuel efficient than petrol engines. Not only that, they have far more torque available at a lower rpm than their gasoline engine counterparts. Diesel Engines also offer lower carbon dioxide emissions per kilometer than petrol engined cars.

Take the case of our first Indian SUV - Tata Safari as an example:

Average fuel consumption for an Intercooled turbo charged 1.9 L diesel Safari: 12.5 km per liter
Average fuel consumption for the 2092 CC Petrol Safari: 7 km per liter
It is the main reason why larger engines are invariably powered by diesel.

Diesel engines have a compression ratio of 20-22:1 compared with 7-9:1 of petrol engines. So the engines have to be bigger and built on sturdier engine blocks. The injection pumps which are critical for the performance of the engine are precision engineered. This makes these engines last longer and require fewer engine overhauls. As these engines have their air intake always open unlike the petrol driven engines, they can idle for longer duration without gulping down the fuel. The low end grunt or the higher torque available at the lower rpm makes the diesel engine haul reasonable load easily at low engine speeds.

Turbo charged inter cooled diesel engines often can surpass the peak power/torque of many naturally aspirated petrol engines of comparable size.

In water logged roads of many parts of India, diesel cars have little chance of dying out due to electrical problems. Another factor which works in favor of diesel cars in monsoon India is the lower exhaust temperatures of diesel engines compared with petrol cars. This would result in fewer problems in the exhaust pipes getting exposed to water.

Disadvantage of Diesel:

Initial price difference is high - by at least Rs.50,000. Engines are heavier than petrol engines resulting in more wear in tires.

Oil changes are frequent - at every 5000 km instead of 10,000 km in the case of petrol engines. Modern common rail technology makes the engine management systems complex rendering the engines serviceable only with their authorized dealers.

But in these days of fuel injected petrol car engines - complex engine management control systems exist in both engine types obviating the need for specialized service facilities.

So the bottom line is - it still depends on the usage. If you commute long distances, drive around often in water logged roads or plan to retain your car for a longer duration - diesel is the best option for you.