DIESELS BANNED IN 4 CITIES
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DIESELS BANNED IN 4 CITIES
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Joined: Nov 2011
Posts: 118
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From: Ohio
2006 E320 CDI
pick your own poison it seems. 
Both petrol and diesel are derived from crude oil, a mixture of hundreds of hydrocarbons — compounds containing mostly carbon and hydrogen, and some other elements like nitrogen and sulphur.
Diesel cars emit less hydrocarbons, carbon monoxide and lead pollution than petrol cars, but produce more noxious gases and significantly more particulates. Despite much debate over which car, petrol or diesel, is cleaner, weighing up the advantages and disadvantages is not easy.
Overall, diesel cars emit less hydrocarbons, carbon monoxide and lead pollution than petrol cars, but produce more noxious gases and significantly more particulates
Petrol cars with catalysts still produce more CO and HC than diesel cars, although exhaust emissions of NOx and particulates are much lower than diesel cars. In fact particulate emissions from petrol cars are so low that they are not routinely measured.
Diesel fuel contains more energy per liter than petrol and coupled with the fact that diesel engines are more efficient than petrol engines, diesel cars are more efficient to run.
Diesel fuel contains no lead and emissions of the regulated pollutants (carbon monoxide, hydrocarbons and nitrogen oxides) are lower than those from petrol cars without a catalyst.
However, when compared to petrol cars with a catalyst, diesels have higher emissions of NOx and much higher emissions of particulate matter.
Most pollutants are produced at start up.
On a cold day a petrol car may take up to 10km to warm up and operate at maximum efficiency; a diesel car may only take 5km. Consequently, diesel cars produce less unburned fuel during a cold start, which will result in lower emissions of carbon monoxide and hydrocarbons.
Diesel cars could make a significant impact on air quality in urban areas where most cold starts occur, especially when it is considered that a catalyst on a petrol car would take several minutes to reach its operating temperature.
Cars built by Mercedes-Benz, for instance, inject an extra fluid called urea to convert NOx into less harmful substances. This approach (called Bluetec) doesn't compromise on fuel economy or power, but it requires a separate tank for the urea, which must be periodically refilled.
Volkswagen invested millions to develop a NOx trap instead. The trap soaks up nitrous oxide and nitrogen dioxide like a sponge. Once the trap is full, the system can inject a dose of fuel before releasing exhaust substances. The fuel reacts with the NOx to form benign substances. Typically, the filter only runs for about 10 seconds, once every 10 minutes. (They may also run their combustion differently at certain points to lower emissions.) In light of recent revelations, however, it looks like Volkswagen made the wrong bet.
Volkswagen may have resorted to cheating because the NOx trap eats up fuel or reduces the car's pep. But Volkswagen owners may end up being disappointed with the more sluggish, gas-guzzling cars they get back.
Future technology?
It's likely that cars of the future will include diesel technology that combines clean-emission techniques, power and fuel economy, Hillebrand said. When engineers analyze the diesel-engine combustion process, they have found that there are some pressures and temperatures that produce high levels of soot or NOx. But some temperature and pressure regimes get efficient fuel combustion without producing either pollutant.
Hillebrand's team is developing low-temperature combustion systems that aim to do just that. These systems either precisely time fuel injection or even use gasoline and diesel fuel at different times in the car's operation to hit that sweet spot, he said. These experimental systems, however, need a lot more engineering before they're a marketable solution, he added.
Both petrol and diesel are derived from crude oil, a mixture of hundreds of hydrocarbons — compounds containing mostly carbon and hydrogen, and some other elements like nitrogen and sulphur.
Diesel cars emit less hydrocarbons, carbon monoxide and lead pollution than petrol cars, but produce more noxious gases and significantly more particulates. Despite much debate over which car, petrol or diesel, is cleaner, weighing up the advantages and disadvantages is not easy.
Overall, diesel cars emit less hydrocarbons, carbon monoxide and lead pollution than petrol cars, but produce more noxious gases and significantly more particulates
Petrol cars with catalysts still produce more CO and HC than diesel cars, although exhaust emissions of NOx and particulates are much lower than diesel cars. In fact particulate emissions from petrol cars are so low that they are not routinely measured.
Diesel fuel contains more energy per liter than petrol and coupled with the fact that diesel engines are more efficient than petrol engines, diesel cars are more efficient to run.
Diesel fuel contains no lead and emissions of the regulated pollutants (carbon monoxide, hydrocarbons and nitrogen oxides) are lower than those from petrol cars without a catalyst.
However, when compared to petrol cars with a catalyst, diesels have higher emissions of NOx and much higher emissions of particulate matter.
Most pollutants are produced at start up.
On a cold day a petrol car may take up to 10km to warm up and operate at maximum efficiency; a diesel car may only take 5km. Consequently, diesel cars produce less unburned fuel during a cold start, which will result in lower emissions of carbon monoxide and hydrocarbons.
Diesel cars could make a significant impact on air quality in urban areas where most cold starts occur, especially when it is considered that a catalyst on a petrol car would take several minutes to reach its operating temperature.
Cars built by Mercedes-Benz, for instance, inject an extra fluid called urea to convert NOx into less harmful substances. This approach (called Bluetec) doesn't compromise on fuel economy or power, but it requires a separate tank for the urea, which must be periodically refilled.
Volkswagen invested millions to develop a NOx trap instead. The trap soaks up nitrous oxide and nitrogen dioxide like a sponge. Once the trap is full, the system can inject a dose of fuel before releasing exhaust substances. The fuel reacts with the NOx to form benign substances. Typically, the filter only runs for about 10 seconds, once every 10 minutes. (They may also run their combustion differently at certain points to lower emissions.) In light of recent revelations, however, it looks like Volkswagen made the wrong bet.
Volkswagen may have resorted to cheating because the NOx trap eats up fuel or reduces the car's pep. But Volkswagen owners may end up being disappointed with the more sluggish, gas-guzzling cars they get back.
Future technology?
It's likely that cars of the future will include diesel technology that combines clean-emission techniques, power and fuel economy, Hillebrand said. When engineers analyze the diesel-engine combustion process, they have found that there are some pressures and temperatures that produce high levels of soot or NOx. But some temperature and pressure regimes get efficient fuel combustion without producing either pollutant.
Hillebrand's team is developing low-temperature combustion systems that aim to do just that. These systems either precisely time fuel injection or even use gasoline and diesel fuel at different times in the car's operation to hit that sweet spot, he said. These experimental systems, however, need a lot more engineering before they're a marketable solution, he added.
