The debates on this particular topic are probably as old as the fuels in question themselves. A bulk of these debates are between the automobile makers on one hand who stress on the virtues of a diesel engine from the point of view of performance and the so called “Green Peace” environmentalists on the other who keep harping on all the pollution caused in the atmosphere. While both sides have their own Ayes and Noes, a person intending to buy a car is confused.
Though I’m no expert when it comes to automobiles and fuels, I certainly know the mechanics involved, having studied all about Internal and External Combustion Engines in my Tenth standard and still remember most of it. I’ll attempt to look at this review with an eye pre dominantly on two factors.pollution and performance.
Pollution
The five main emissions or pollutants spewed out from both a diesel vehicle and a petrol vehicle are:
Carbon Dioxide – Probably the main cause for concern at the moment, it has been recognised around the world that it causes global warming. Though this does not directly affect our health, it certainly plays a major role in changing the climatic conditions around us. Carbon dioxide emissions are directly proportional to the fuel consumption, and because diesel cars use around 30% less fuel than petrol cars, they emit that much lesser carbon dioxide.
Carbon Monoxide - Carbon monoxide is a lethal poison but has the capacity to kill humans within no time. Most of us would have inhaled this at some time or the other when we run a petrol car engine in a closed space like a garage. Since diesel engines produce virtually no carbon monoxide, they are that much safer. To counter this petrol car makers have come out with Catalytic Converters but the main problem here is that these converters take nearly 15-20 minutes to warm up and function effectively.
Nitrogen Oxides - Nitrogen is the main constituent of the air that we breathe and when exposed to high pressures and temperatures it combines with oxygen in the air to form nitrous oxides. The nitrous oxides then combine with low level ozone to form smog which is so common in Delhi and Mumbai. Tests of cars reveal that whilst emissions of Nitrogen Oxides are higher in a new diesel than a new petrol car but by 50, 000 miles or so they are the same, and after that the petrol engine produces more Oxides than the diesel car.
Hydrocarbons – The Hydrocarbons in fuels include chemicals such as benzene. Benzene is an stated to be an extremely carcinogen chemical and has been declared unsafe by the WHO. Hydrocarbon emissions are contained in petrol engine emissions much more than in diesel engine emissions.
Suspended Particulate Matter(SPM) - SPM refers to solid particles suspended in open air, such as soot generated by combustion of various fuels(both from industries and automobiles). Diesel engines emit more PM10 particles, that is particles which have a diameter up to 10 microns. These SPM are supposed to be carcinogenic in nature but a lot of research and tests across the world have not been able to prove it so far. What has been proved is the fact that they do cause respiratory problems because of their tendency to deposit themselves in the lungs.
Out of the five emissions, Diesel engines come out tops with regards to Carbon Dioxide, Carbon Monoxide and Hydrocarbons. Both fuels are more or less the same when it comes to Nitrogen oxides and Diesel certainly is dangerous from the point of view of SPM.
Performance
Efficiency – Diesel engines are considered to be more efficient than petrol engines because they use a higher compression ratio and work at a higher temperature which causes fuel to be burnt completely thus extracting the most out of it without any wastage.
Maintenance - Diesel Engines use a higher compression ratio compared to the petrol engines as a result of which the vibrations in a diesel engine are higher and cause the wear and tear of the different parts of the engine. The design and construction of the diesel engine is however much simpler and more robust than the petrol engine. As long as the vibrations are kept in check, the diesel engine is just as reliable as its counterpart. A prime development of late has been the arrival of’common rail’ diesel technology which offers a more controlled fuel burn. Another advance has been in the area of turbo charging. This also causes a reduction in the’diesel knock’ caused by the engine’s high compression ratio by effectively absorbing the vibrations.
Reliability – The most common grouse against diesel engines has been that they take a long time to start during the winter season because the engine works only at a high temperature. It is also true that more often than not, petrol cars fail to start during the monsoons thanks to a lethargic plug which is unwilling to give out a spark. How many times have we faced the herculean task of having to trudge home with the two-wheeler in tow only because the spark plug went for a toss? Though the diesel engine takes time to start during winter, it does start and moreover, it faces no problems during monsoon too thus making it a better proposition.
Price and Mileage – Diesel is nearly half in price as compared to petrol and is therefore easy on the pocket. They also give substantially more mileage as compared to the petrol version. As for those planning to purchase a car in the near future, bear in mind that a diesel car makes sense financially only if the annual mileage is more than 13, 000-15, 000 Kms. If you feel that your annual mileage will be less than that, close your eyes and opt for a petrol version. One also needs to take a futuristic view on the proposed levy of additional tax on diesel, for if that falls through, the overall maintenance of a diesel car would definitely be costlier.
Of late there have been some sweeping changes with regards to the preference for petrol cars with the Supreme court conclusively ruling that diesel vehicles be banned from plying on the roads in and around New Delhi. For all the accusations that diesel engines are far more polluting and difficult to maintain, one simply cannot wish away diesel as a fuel because it still remains the sole food for Commercial Vehicles, especially the heavy ones. What perhaps can be done is to minimise the polluting effects of both petrol and diesel as also further explore the possibility of large scale substitution of these with LPG and CNG.