Cars that run on powertrain, utilise an internal combustion mechanism and run on diesel are more fuel efficient than petrol vehicles. Simply speaking, diesel powertrain is a compression ignition unit, which means that the fuel is ignited by exposing it to a high level of temperature suddenly and introducing pressurised compressed gas. It does not use a separate combustion source, as is the case of a petrol engine, which uses a spark plug for the same purpose.

Are diesel cars more fuel efficient than the petrol or CNG cars?

Diesel cars usually offer more mileage then their petrol counterparts but lesser than CNG vehicles, though their power and torque is much more than that of CNG cars. Diesel models offer maximum energy efficiency of 41 per cent; however, on general basis it offers 30 per cent as compared to 37.3 per cent maximum efficiency of petrol cars and 20 per cent general energy efficiency. This is the underlying reason for why diesel car offers better mileage than the petrol vehicles. An efficient turbo-diesel powertrain unit offers as much as 25 per cent more mileage compared to its petrol counterpart.

For example, the powertrain serving on the existing Skoda Octavia offers a mileage of 17.5 kmpl for the petrol unit, which delivers 105 bhp, and 22.2 kmpl for the diesel unit that churns out the same output. The diesel models offer higher compression ratios which in turn assist in increasing the energy efficiency of the car. Diesel also offers 10 per cent additional energy on every unit volume as compared to petrol, thus providing better mileage keeping in mind the given power output.

Are there any performance differences between diesel and petrol cars?

Petrol, being more inflammable of the two fuels, offers more horsepower and ensures better performance at higher rpm counts. In petrol cars, the fuel is first compressed and then ignited using a spark plug. The smaller the engine is, the better is the fuel efficiency. On the other hand, diesel is not as inflammable and, thus, cannot be ignited using a separate mechanism. The diesel powertrain compresses the fuel to such an extent that it heats up and ignites by itself. This is the reason that such powertrains are bigger and ensure longer life and dependability. They are generally used in load carriers like trucks and vans because they have more torque at their disposal to ensure better low-end power.

Which fuel option is more economical to own in the long run?

There are three important points to be kept in mind while considering a vehicle that impacts the overall cost, viz. price of the vehicle, running cost (fuel expense) and the maintenance cost. Another factor that affects the costs in the long run is 'time'. Diesel cars are not the right choice for people who like to change their cars every 2-3 years. In terms of price, a petrol car is the cheapest option, followed by CNG and then diesel cars. The latter has a cost differential as high as Rs. 80,000 to 1 lac as compared to petrol powered vehicles.

Considering the average mileage offered by diesel, petrol and CNG cars (21, 14 and 16 kmpl, respectively), it could take the owner at least 18-19 months to recover the price of the car. On the other hand, it normally takes around 3-4 years to break even the investment on diesel car considering the additional price. Moreover, there is additional repair and servicing cost that a diesel car commands as the frequency of maintenance is higher with these vehicles.

Diesel Cars in India