Why are diesel engines more efficient than gas engines?
We get this question a lot, as people often associate diesel engines with semi-trucks and large pickups that don’t seem to represent fuel efficiency. Yet diesel passenger cars on the market now, like the Volkswagen Jetta TDI and Mercedes-Benz E-320 CDI, do have gas mileage ratings on par with much smaller compact cars that use less-powerful gasoline engines.
According to an Automotive Service Excellence representative, diesel engines — whether in a semi or a Jetta — are more efficient because of the diesel engine process, which burns fuel at a much higher temperature than regular gasoline engines, promoting more-efficient fuel combustion.
Also, diesel fuel has a higher energy density than standard gasoline, meaning it takes less fuel to provide the same power as standard gasoline.
There are a couple of reasons why diesel engines in passenger cars haven’t gained popularity in the U.S., even though they are efficient. Besides the fact that not every gas station has a diesel pump, there are also the stigmas of soot-puking tailpipes, oily fuel residue and noisy engine clanking associated with previous generations of diesel cars. Today’s modern diesel passenger cars are surprisingly quiet, as well as clean burning, and produce little or no tailpipe soot due to advancements in engine technology and the new clean-diesel fuel that is now the only diesel fuel sold in the U.S.
Learn more
diesel cost more. a great deal more. how much does cost per mile?
Hi out there myself I have a 2006 bmw 730D TURBO and fuel consumption is brilliant urban 9L per 100km and intercity 6-7L per 100km power is emence and 520Nm torque compare 6L petrol 600Nm.
Service free brakes etc. 100.000km or 5 years.
ur cars are cool.
Valid point about diesels gelling in the winter. this problem is easily solved by supplementing you diesel fuel with an inexpensive bottle of diesel treatment/anti-gel, though.
When a gas expands whilst doing work against a piston, it cools.The energy of motion of the molecules has lessened because some of it has added to the motion of the piston. In a diesel there is more expansion than in a petrol engine becuse the compression ratio is say 20 to 1, for petrol engine 10 to 1. Because the gas expands more it must cool more so the exhaust gas is cooler than in a petrol engine. The difference in temperature between the gas at the start of combustion and at start of exhaust gives you the efficiency of the engine. The bigger the difference the more of the heat energy has gone into moving the piston - "useful work" The extra energy density of diesel wouldn't make the engine more efficient without the above process.
Thank you, richard ford. Great explanation.
Another reason the diesel cycle is more efficient is because there is no ignition system to energize. As for the higher price of diesel fuel, that is due simply to a higher tax structure. Diesel fuel actually costs less to produce because it is refined less than gasoline ( which also explains why diesel is more energy-dense).
If the government wanted to reduce our consumtion of middle est oil. They should drop the price of diesel fuel, and require automakers to put standard diesels in most cars. I don't think they really want diesels because they are making a killing off of these oil companys. Diesels are very durable, efficient, and powerful.
Diesels are not as clean as this article suggests.
The Mercedes E320 Bluetec that they mention is not even legal in California.
See if your question has already been asked and answered
Your question has been successfully submitted to Ask.cars.com. It will now be reviewed by our editors and we'll answer it soon if we think it's a useful question. You will be notified via e-mail when the answer is posted. Ask.cars.com tackles your questions about new cars and the car-buying process. Unfortunately we can't answer questions regarding:
Have our experts answer any of your questions about new cars.
Don't worry — we won't publish your last name or email.
Another idea held onto from old diesels is that they don't start in the winter. New diesels are pretty reliable in the cold. However, diesel does gel at higher temperatures than gasoline, so in extreme cold, that problem can still occur.