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Diesel dilemma

Discussions centering on energy-efficiency levels and emissions reduction continue to dominate the automotive industry and its powertrain subsector. As a result, one would assume that the diesel engine is set to have a brilliant future, but there do seem to be some doubts.

In Europe, diesel-powered passenger cars have become big business, especially since the introduction of direct-injection technology, which has allowed for increases in power output but decreases in fuel consumption and emissions, making the diesel engine an attractive option over gasoline units. In some European countries, diesel engines account for more than half of all new car sales. And the diesel trend in Europe further gathered momentum following the introduction of variable turbocharger systems and increasing injection pressures.

But with popularity came grave concerns. The diesel engines were seen as being unclean in terms of PM, NOx and CO2 emissions. Diesel cars were blamed as smog lingered over European cities. Even the urea and Ad-Blue image that the likes of Daimler, Chrysler and Volkswagen Group are trying so hard to market in the USA is struggling. The real problem is that the introduction of the particulate traps came too late to head off those that questioned diesel technology and helped to establish its not-so-clean reputation.

On the other hand, a modern diesel engine is a modern engineering masterpiece packaged with two-stage turbos, emissions-reduction systems with cooled low-pressure EGR, 2,000 bar common-rail technology, injection and combustion strategies, particulate filter and an SCR catalyst. The problem is that such a package is an expensive piece of kit for all concerned – OEM, supplier and consumer.

Ironically, the bad news for diesel is that the situation is changing. Gasoline engines with direct injection, turbocharging and variable valvetrain are now coming into similar areas of power and torque. With prices of diesel fuel now approaching the same level as that of gasoline, those backing diesel technology are under pressure to bring to market a new wave of systems that can increase the engine power, enhance consumption, and reduce emissions.

In order to meet these three requirements, more has to be done in the R&D labs. An evolutionary way forward is simply not enough. The friction losses are too high and there are generally too many losses from the auxiliary drive. Admittedly, turbocharger systems hold a lot of potential – there may even be the possibility to connect the turbocharger with an electrified powertrain.

It is clear that downsizing is becoming a favored option for OEMs. Concept cars have been shown that feature two-stage turbocharged four-cylinder diesel engines connected with hybrid drive. Such a system could replace the traditional, gas-guzzling V8. This is a step forward to reduce fuel consumption and not to increase cost by a great margin, The problem will be meeting the tight emissions standards. The question therefore is, should energy consumption at a low NOx emission level be a high priority? Should the gasoline engine follow the route into lean combustion, then face the same problems? Or should the solution focus on overall lowest emissions standards, looking to other technical areas, such as electromagnetic valvetrain?

For me, there is no doubt that both gasoline and diesel engines will be around for a long time. From a purely emotional perspective, many drivers still love the thrill of V engines. My BMW V10 is great fun and is something I want to continue to enjoy in the future, despite having to take into consideration emissions legislation. 

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