Long gone are the days when diesels were thought to be highly polluting engines with emissions consisting of a great quantity of carcinogenic particulate matter. Besides, the efficient direct injection engines were not able to reach high revolutions per minute apart from being very poor on the noise, vibration and harshness parameters. The efficient direct injection engines were thought to be highly unsuitable for passenger car applications. All that has long since changed.

It was a diesel that broke the 3-litre barrier in the shape of a small turbocharged unit in the Volkwagen Lupo. Not only have diesels set the benchmarks in terms of fuel efficiency, they have also demonstrated that they can be right up there with the best that petrol engines have to offer. The new V10 313bhp diesel that Volkswagen presented on the occasion of its 25th anniversary earlier this year produces some 750Nm of torque. This compares very favourably with the 6-litre 48-valve W12 petrol engine that produces maximum power of 420bhp and rated for a maximum torque of 550Nm.

And if you consider the impact of internal combustion engines on environment, after a seesaw battle which has swung either way over the last few years, the modern day diesel engine is now considered to be more eco-friendly of the two. Even though diesel engines are more efficient than petrol ones because of an excellent thermodynamic performance due to a higher compression ratio, have better combustion because they operate with excess air and avoid energy losses linked with butterfly back pressure on the inlet gases under partial load, they have been under a cloud because of the particulate emissions. What has tilted the balance in the favour of diesels is the new particulate filter which is regenerative. These types of regenerative particulate filters were first introduced by PSA Peugeot Citroen on its high-pressure direct injection (HDi) engines. Similar technology has since been unveiled by other companies like Toyota.

Diesels have an edge over petrol engines since they are more efficient, burn lesser quantity of fuel to do the same work as petrol engines and therefore produce less carbon dioxide. Besides as engines age the emissions of petrol engines increase dramatically as compared to an imperceptible increase in emissions from diesel engines. It therefore comes as no surprise that the NZEV (near zero emission vehicle) that Fiat has been working on also has as its base a direct injection diesel engine. Fiat is using variable valve actuation along with multijet injectors to combat the problem of emission from diesel engines. Fiat is already onto its second generation common rail direct injection system that uses the newly developed multijet which effects sequential multiple injections providing a more even temperature in the combustion chamber and inhibiting the formation of particulate matter. Further work is also underway on engines that do not need oil changes and here too, the diesel is out in the front. Engineers at Daimler-Benz have already achieved oil change intervals that are over 10 times than what they used to be a few decades back. While petrol engines which would need an oil change between 14,400km and 20,000km are already in the market so are diesel direct injection engines that would need an oil change only after 40,000km or two years.

After reading all this I don't think that you would find it hard to believe that close to 40 per cent of the passenger cars sold in Europe are diesels. This despite the prices of petrol and diesel being just about the same as are the prices of new cars. The gap is closing every year and there will soon come a day when there will be more diesel-engined cars than petrol-engined ones being sold in Europe.

In India the scenario is quite dismal. While on one hand the high petrol prices have prompted car manufacturers to get in technologies that are efficient, the subsidies on diesel have let the diesel engine technology languish at abysmal depths. Because diesel engine technology in India is from a prehistoric era, people's perception of diesel engines is also very bad.

It is only now because of the emission control norms that diesel engine makers are being forced to upgrade technologies. The simplest and cheapest way of doing that is to turbo-charge the engine. Turbocharging is welcome because it makes the engine more efficient. Telco, the largest manufacturer of diesels now has turbocharged engines for its commercial vehicle range, its utility vehicles and is soon going to launch its passenger car with a turbocharged diesel. The other UV manufacturer M&M also needs to follow suit and naturally aspirated diesels should soon become history. Next is the step forward to direct injection. For DI engines to be acceptable on passenger cars, the manufacturers will have to adopt some of the latest technologies like common rail or unit injector systems because the current crop of DI engines in the country do not suit applications where NVH considerations are paramount.

But do not be disappointed. There are already some great hi-tech engines making there way into the country, albeit in some of the higher end cars. The first to arrive on the scene was the common rail diesel on the Mercedes-Benz E220 CDI. The inline four cylinder 16-valve engine is a delight as is the C200 CDI one. Then there is the 2.0-litre Duratorq DI 16-valve turbodiesel on the Ford Mondeo that we cannot stop raving about. Lower down the affordability stakes is another excellent 1.9-litre common rail electronic direct injection engine that will do duty on the Skoda Octavia 1.9 TDI. Drive any of these cars and you will change your opinion about diesels. But what I am waiting for is the advent of such a hi-tech engine into one of the small cars. That will be the day when a Zen gives 40km per litre of diesel! Anyone wanting to oblige? Why don't you take the lead Telco?