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Redesigned diesel engine can be a green-friendly choice

Dear Car Fix: What is your take on diesel vs. gas engines in vehicles today? Diesel fuel mileage is better, longevity of the diesel engine is better, pollution is reduced. Why is it just the Germans bringing diesel to the market?

BMW, MB, VW/Audi all have highly fuel-efficient diesels in small cars, wagons, sedans and sport utility vehicles. U.S. manufacturers have to look past 3/4 -ton trucks and start introducing diesels into the lighter duty trucks and even into larger sedans and/or small cars. Everyone thinks ethanol is the answer to the energy crisis. Electric hybrids aren't the answer either. Just wondering where you stand.

-- P.M., Lancaster

Dear P.M.: I'm a huge diesel fan, and I agree that this is a better solution than electric hybrids or ethanol by a long shot.

Environmental impact: While hybrids might be the green champions, clean diesels can be just as friendly to the environment -- possibly even friendlier. That conclusion takes into account that diesel engines use less fuel to make an equivalent amount of power, and less overall consumption equates to lower carbon dioxide emissions. Also, disposing of batteries from hybrid vehicles is a challenge that could prove more difficult than we know.

Different fuel, engines and pollution: Basically, diesel fuel contains more potential energy than gasoline. The compression-ignition engines in which diesel burns have higher compression ratios than gasoline engines, which makes them produce more power for an equivalent amount of fuel. Gasoline is more highly refined and burns inherently cleaner and it is available in all the 161,000 retail fuel stations in the U.S.; "clean" diesel is available in about half of those.

In 2007 the U.S. government standards for diesel fuel required that it contain far less sulfur, thereby allowing manufacturers to create sophisticated engines that burn diesel cleaner. The dramatically reduced exhaust emissions in diesel vehicles meet the same emissions standards as gasoline autos.

Diesel vs. hybrid: Hybrid vehicles on the market today are powered by gasoline, and they are assisted by electric motors during those times when using a gasoline engine is least efficient. In a hybrid vehicle, the engine is shut off at each stop and the vehicle will start on its electric motor using power stored in a large battery. The more often the vehicle is stopped, the more efficiently it will use its gasoline.

The so-called "two-mode" hybrid vehicles actually use two electric motors to propel or capture decelerating energy, and to create optimum gearing for the gasoline engine on long-distance travel. Single-mode hybrids almost always get better fuel efficiency in slow, heavy traffic than they do on the highway. Two-mode hybrids are more efficient on the highway.

Diesel vehicles take advantage of the characteristics of more powerful fuel, and can idle using relatively small amounts of fuel. That means in heavy traffic, with lots of stop-and-go progress, fuel is being wasted. However, at higher speeds and for longer-distance travel, similarly sized diesel vehicles will get better fuel efficiency than gasoline-powered hybrid vehicles.

The power advantage: As well as using less fuel to produce the same power as a gasoline engine, diesel engines also make that power in a lower rev range in their engines. The amount of torque the engine makes, which is the ability to tow and haul, is available at lower speeds and in a greater amount than a gasoline engine. Electric vehicles have no torque to pull a trailer. That means driving uphill, towing a trailer and overtaking another car are inherently easier for a diesel vehicle versus a gasoline-only vehicle.

To run as cleanly as a gasoline engine, a diesel engine must be equipped with more sophisticated fuel injection and several means to clean the exhaust after combustion takes place. Therefore, the engines are more expensive to produce. There is evidence, however, that they will last longer than gasoline engines.

To enable the vehicle to run on electricity only, a hybrid must have a large, heavy battery aboard. Very sophisticated power controllers sense and regulate the amount of electricity sent to the motor that assists the gasoline engine. The weight of the battery almost always makes a hybrid heavier than an equivalently sized diesel vehicle, which reduces performance. Diesel vehicles achieve their best fuel efficiency on long trips and hauling loads, and for performance driving.

The good news is that Chevrolet is planning a 2013 Cruze Diesel that they claim earns 50 miles per gallon. I'm impressed that GM took the first step to be the first U.S. company to make the diesel push.

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