Powering the Indian Automobiles: Diesel or Petrol and Euro 4 or Euro 6?

Traditionally, technological trends the world over had favored petrol engines for the lighter passenger cars and diesel engines for the heavier trucks and buses. Petrol engines are lighter and quieter, and capable of developing more power, making them an ideal choice for the lighter vehicles such as cars. They are high-revving and have better power to weight ratios and have nippy acceleration. Diesel engines are heavier and noisier, but capable of developing more torque, making them an ideal choice for the heavier vehicles such as trucks and buses. Diesel engines are low-revving and have better torque to weight ratios, and have greater moving force.  Modern developments in engine technologies, however, upgraded the diesel engine to greater efficiencies, suitable for lighter vehicles too. Europe has pioneered this light diesel engine technological revolution, as evidenced by France having 77 percent of cars as diesel driven, followed by Germany at 44 percent. Japan with its passion for clean and quiet environment has been a great respecter of petrol engines; Japan has only 2 percent as diesel driven cars. US has been at the other extreme, encouraging use of gasoline even for trucks and buses.

India has, surprisingly, already 49 percent of its cars as diesel driven cars. The equal share of diesel prime movers in India has not been due to contemporary diesel engines, until at least the recent years. The share of diesel engines in passenger cars has been driven almost entirely by the differential pricing of petrol and diesel, with the former being more or less market driven and the latter being administered, ostensibly to keep the truck and bus transportation costs low. The oil industry/the government loses roughly Rs 26 per liter of diesel, which is also approximately the cost saving per liter of diesel. Notwithstanding the noisy and dated technologies, diesel driven vehicles have started gaining popularity in India. Today, no utility vehicle (UV) in India comes with a petrol engine option while passenger cars, even smaller hatchbacks, also have taken to offering diesel engines predominantly. This has, not surprisingly, led to a public debate on the entire gamut of fuel pricing, vehicle taxation and use of diesel engines in automobiles.  

Public debate

Diesel engines emit darker smoke with higher particulate matter. As if this was not enough, diesel exhaust was classified by World Health Organization (WHO) in 2012 as a class 1 carcinogen, placing it in the same toxic bracket as tobacco smoke. A recent All India Institute of Medical Sciences (AIIMS) study found growing incidence of lung cancer in non-smokers in Delhi. The study hypothesized that exposure to diesel exhaust fumes could be one reason. The environmental voice against the dieselization of cars is forcefully heard from Centre for Science and Environment (CSE) chief Sunita Narain, who states “it is immoral of the auto industry to create demand for a fuel that makes oil refineries bleed and our lungs explode”. She argues that diesel has to be a confined as a fuel for public utilities. Some experts have proposed higher taxes for diesel cars, in terms of higher excise duty, annual tax on diesel cars and so on.  Others have proposed total decontrol of petrol and diesel prices. Diesel pricing, being a politically sensitive issue, no major change in differential pricing may be expected anytime soon.    

The public itself seems indifferent to the debate on the risks of diesel engines and continues to favor diesel engines. A diehard petrol car maker like Honda is now forced to introduce for India a diesel car named Amaze. The automobile industry says that passenger cars are a small contributor for the air pollution on the roads, laying the blame on the aged commercial vehicle population of the country. It also maintains that consequent to the change from Bharat Stage III (BS III) emission norms to BS IV emission norms, the permissible particulate matter discharge has been brought down from 0.5 grams per kilometer to 0.025 grams per kilometer in diesel cars. Non-introduction of BS IV norms across the country is frowned upon by the industry experts. Lack of smog in Europe, which runs predominantly on diesel engines is pointed out in defence of smoggy pollution of India being caused by factors other than diesel cars.

A recent Central Pollution Control Board (CPCB) study threw up important findings. According to the study, vehicles contribute only 6.6 percent to particulate emissions (PM) in Delhi. Road dust is the biggest contributor at 52.5 percent while industries contribute 22 percent and geography 19 percent. The contribution of road dust to PM pollution is a rampant concern across India. The sharp rise in PM10 (respiratory particulate matter) levels and the NOx (nitrogen oxide) levels are both attributable to public and industry apathy, it looks. Even with BS IV norms, the diesel emission levels are still far more than those of a petrol engine. Public and regulatory options must recognize the operating fuel price incentives available for preferring diesel cars and the lack of incentives for producing more efficient and environment-friendly diesel engines and cars . While the equalization of diesel and petrol pricing is a policy option with several undertones, the automobile industry and the oil industry must take the lead for technological solutions. 

Engine technologies 

The key to finding the right driving and emission options lies in the engine technologies. Diesel engines which are compression ignition engines have to be more rugged (bulkier, heavier and noisier), with the engines designed to meet the pressures needed to compress air to diesel ignition temperatures. This is compounded by the need for precise injection of diesel fuel in each of the cylinders. The introduction of common rail diesel system in diesel engines coupled with electronic injection of fuel has resulted in better combustion efficiency and better combustion balance across cylinders. These developments need to be pursued further to ensure more complete combustion of the diesel fuel. The injection technologies themselves need to be sharpened to ensure greater micro-mixing of fuels. The engine technologies, coupled with ultra-low sulfur diesel would help the efficiency cum emission cause. The choice of diesel engines currently available in India for passenger car applications is too small to evoke these competitive technological forces.  Indian manufacturers and the collaborators/parent corporations would need to bring in their best of diesel engine options to India to reposition the diesel engine technology based on performance and emission levels rather than on price and cost basis.

Ultra low-sulfur diesel 

Ultra-low sulfur diesel (ULSD) is diesel fuel with 15 parts per million or lower sulfur content. The US Environmental Protection Agency (EPA) requires 80% of the highway diesel fuel refined in or imported into the United States (100% in California) to be ultra-low sulfur diesel. One hundred percent was mandated to be ULSD nationwide by 2010 in USA. Ultra-low sulfur content in diesel fuel is beneficial because it enables use of advanced emission control technologies on light- and heavy-duty diesel vehicles. The combination of ULSD with advanced emission control technologies is sometimes called "clean diesel". Nitrogen oxides and particulate matter are the two most harmful diesel pollutant emissions. These emissions can be controlled with the use of catalytic converters and particulate traps. However, sulfur—in amounts that used to be allowable in diesel fuel—deactivates these devices and nullifies their emissions control benefits. Using ULSD enables these devices to work properly. In India, the national capital Delhi first introduced ULSD on April 1, 2010 as a step aimed at curbing vehicular pollution in the capital. However, the rollout of ULSD elsewhere as also modernization of the fleet on the roads or the use of pollution control equipment have been tardy, nullifying the potential benefit of ULSD.

Emission gap

India is on BS IV for emission norms, considered aligned with Euro IV emission regulations. The point to note is that while India is yet to achieve a nation-wide coverage of BS IV norms, Europe has already implemented Euro 5 norms and is committing to deploy Euro 6 standards by 2014.  Diesels have more stringent CO standards but are allowed higher NOx emissions. That is undergoing a significant squeeze. In respect of diesel engines, CO limits have been reduced to 0.5 gms per km in Euro 4 itself while NOx limits have been reduced from 0.25 gms per km in Euro 4 to 0.18 gms per km in Euro 5 and as low as 0.08 gms per km in Euro 6. In fact, NOx limits for diesel engines are now almost on par with those of petrol engines, indicating the huge strides diesel engine technologies would need to take meet the futuristic emission norms. In contrast, BS IV norms are yet to be rolled out beyond the National Capital Region and 13 major cities. If India takes the lead to leapfrog to Euro 6 norms, in respect of both diesel and petrol engines, clearly there would be a transformational change in the emission scenario of India.

Holistic approach

The increasing share of diesel engines in the Indian passenger car industry and the emission implications thereof can only be inadequately and somewhat improperly countered by manufacturer-driven price premiums on government driven additional taxation on diesel cars. The fuel pricing differential must be moderated and subsidies by the exchequer on fuel bills reduced. This would be a better option than keeping the subsidies on and seeking additional tax revenues. Manufacturers should be incentivized to invest in superior diesel and petrol engine technologies that meet first Euro 5 norms, and then Euro 6 norms, which should be introduced as early as possible with all-India applicability. The use of ultra low sulfur fuel must extend across the nation. And, most importantly, the nation as a whole, the governments as well as the society, must wake up to the urgent need to curb the menace of rampant atmospheric dust pollution.

Posted by Dr CB Rao on January 7, 2013