Today's Improved Diesel Engine Technology

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Diesel 101: Part 2

By Bill Siuru

If you haven’t driven a diesel powered car lately, you would be surprised at how much they have improved. Gone are clanking engines, smelly exhaust, and anemic performance.

Diesel rattle is eliminated by a combination of direct injection (DI), common rail (CR) fuel distribution, unit fuel injectors, and pilot injection. With DI, fuel is injected directly into the cylinder rather than into a small side chamber as with older indirect injection (IDI). This helps provide the fine, high-pressure mist of fuel needed to eliminate knocks and rattles. High pressure also means better fuel atomization, resulting in increased engine efficiency for more power and better fuel economy

The common rail system uses an engine-driven pump that produces extremely high pressure fuel delivered to the electrically-operated injector at each cylinder, via a single thick-walled tube – the “common rail.” Besides reducing characteristic diesel noise, the CR system can greatly increase injection pressure over the older distributor pump type of injection systems, thus injecting a far finer mist of fuel to enhance DI engine efficiency.

Diesel fuel has to be injected at very high pressures to counter the huge compression pressure in the diesel engine. The higher the pressure, the more power is produced and the cleaner the exhaust emissions. Another advancement is pilot injection, which injects a small amount of fuel prior to the main injection, resulting in a more gradual increase in combustion chamber temperature. This eliminates the diesel knocking and rattling caused by a sudden increase in temperature. All this is made possible by sophisticated electronic injection control systems.

Today’s diesel engines are usually turbocharged and most are intercooled. Turbochargers compress the air supplied to the engine, or in automotive terms, improve engine “breathing.” More air means more fuel can be combusted, leading to increased power output. Exhaust gases spin the turbocharger’s turbine at speeds of up to 150,000 rpm, which rotates an air pump that provides a “boost” of air higher than atmospheric pressure for more powerful combustion. Because the turbocharger is driven by engine exhaust, temperatures are very high. Countering this is an intercooler, either an air-to-air or water-to-air heat exchanger, that’s used to cool down the hot compressed air exiting the turbocharger. Cooler air takes up less volume, so more air can be delivered to the cylinders to produce more power.

Recognizing American’s demand for vehicles offering good fuel economy without compromising utility, cargo capacity, and performance, Mercedes-Benz is one of those leading the way by offering several diesel models. The E320 CDI, which has been offered for several years, has been replaced by the E320 BLUETEC luxury sedan. The E320 BLUETEC is the only diesel-powered luxury sedan available in the U.S. that can deliver an estimated 780 miles on a tank of fuel. In addition, there is the new ML320 CDI, R320 CDI, and GL320 CDI – all SUVs. As of now, these four diesel models are not available in California, Maine, Maryland, New York, and Vermont because they do not pass the more stringent emission requirements in these five states.

The Department of Energy estimates that a 30 percent market penetration of light-duty diesel vehicles by 2020 would reduce U.S. net crude oil imports by 350,000 barrels per day. In California alone, gradually increasing the use of currently-available clean diesel technology in cars, pickups, and SUVs to levels seen today in Europe could save the state 110 million gallons of gasoline per year by 2010, and up to 840 million gallons per year by 2030.

Diesel is on the rise in America: The forces holding it back – namely long-held stigmas and emissions concerns – are quickly being overcome by technology and now, of course, cleaner diesel fuel.

A new generation of clean diesel vehicles selling in large numbers opens the door for biodiesel to play a bigger role as well. This clean-burning fuel is derived from domestically produced agricultural products and runs in a diesel engine with little or no modifications, reducing both emissions and energy dependence.

Plus, diesels could factor favorably into the future of the popular hybrid as well. Just imagine the fuel economy that could be achieved by combining the fuel-saving benefits of hybrid-electric technology with an inherently efficient diesel engine. For example, DaimlerChrysler has developed a “mild hybrid” that combines the 3-liter BLUETEC V-6 diesel with a high-torque electric motor. With all this potential, we expect to be hearing a lot more about diesel in the years ahead.