Automakers developing efficient engines that overturn fuel's dirty image

Diesel-powered vehicles used to get a bad rap for being noisy, dirty and slow. But they have been getting an image makeover thanks to "clean diesel" that emits less pollution--a change that could shake up the race with eco-friendly hybrid and electric vehicles.

At the Tokyo Motor Show in December, there were many "oohs" and "aahs" around the displays of two Mazda Motor Corp. vehicles powered by a 2.2-liter diesel engine--a world first. The fuel-efficient engine can reduce emissions that cause air pollution, without an expensive purifier.

The CX-5 sport-utility vehicle, which will go on the market Feb. 16, runs 18.6 kilometers per liter of diesel oil, a fuel cheaper than gasoline. The CX-5 is the most fuel-efficient SUV, including minicar SUVs and hybrid SUVs, and packs as much power as a four-liter gasoline-powered vehicle.

The Takeri concept sedan stores energy generated during braking as electricity. According to Mazda, it can travel about 1,500 kilometers on a full tank of fuel.

"Diesel vehicles had the shortcomings of being dirty and slow. We've conquered those problems," Mazda President Takashi Yamanouchi said.

The diesel SUV market is becoming rather crowded. Germany's BMW AG will introduce a diesel model of its X5 in Japan this spring. Nissan Motor Co.'s X-Trail and Mitsubishi Motors Corp.'s Pajero are already equipped with clean diesel engines.

With more diesel-powered vehicles arriving in showrooms, some drivers will likely be giving diesel vehicles a second look.

Diesel vehicles and gasoline vehicles produce their power quite differently. In gasoline vehicles, gas is mixed with air, and this mixture is injected into a combustion chamber and ignited. In diesel vehicles, air is compressed until it reaches a high temperature, and diesel oil is then injected into it and burned.

Diesel vehicles are powerful--and more fuel-efficient--even when driven at a low speed because their combustion efficiency is better than that of gasoline vehicles.

However, diesel vehicles emit nitrogen oxide and soot, and they need a big, tough body to handle the volume of air being compressed. They tended to be noisy and had poor acceleration.

Japan experienced a recreational vehicle boom in the latter half of the 1980s, and diesel vehicles accounted for 6 percent of total new car sales. However, their popularity waned and automakers stopped introducing new diesel models, except for buses and trucks.

In the latter 1990s, European automakers developed cleaner diesel engines that produce less exhaust gases by improving the fuel injection system and using filters.

In Europe, fuel-efficient, diesel-powered vehicles have become very popular, accounting for half of new car sales.

Diesel oil is obtained with gasoline during the process of refining crude oil. Because Japan cannot consume all the diesel produced here, some is exported. The spread of diesel vehicles in this country will lead to more efficient use of diesel oil.