Clean Diesel: High MPG, Low CO2. Is it the Next ‘Big Thing?’

Today, diesels are being purchased in huge numbers by Europeans, with diesel models estimated to represent more than half of all new vehicles being sold there. Contrary to what you might think, these are not just small, entry level diesel vehicles, but also upscale diesel-driven rides like the BMW 7-Series, Jaguar S-Type, and Alfa Romeo 156.
This is in stark contrast to the diesel scene here in America, where nationwide diesel choices are more limited. However, a growing number of models have come to U.S. shores in recent years following nationally-mandated low-sulfur diesel fuel, which has made ‘clean’ diesel vehicles that meet stringent emissions standards possible.

Here, we have diesel pickups along with passenger vehicles like the Audi A3 and Q7; BMW 335 and X5; Mercedes-Benz E-Class, GL-Class, M-Class, and R-Class; and VW Jetta, Golf, and Touareg. Model choices have been expanding because of the growing demand for high fuel economy vehicles of all types … an area where diesel excels.

THE DIESEL DIFFERENCE Both gasoline and diesel powerplants are internal combustion engines, although they operate with significant differences. A gasoline engine runs on the Otto cycle, in which a vaporized mixture of gasoline and air is delivered to the combustion chamber, where it’s then compressed and ignited by a spark plug. In the Diesel cycle, air is compressed during the compression stroke and fuel is injected into hot, compressed air in the cylinder, spontaneously igniting the fuel. Because of this, the diesel is sometimes referred to as a compression ignition engine in contrast to a gasoline spark ignition engine.

There are also significant differences between diesel fuel and gasoline. For starters, diesel fuel requires less refining – and thus less energy to create – than gasoline and is similar to kerosene, jet fuel, and heating oil. Indeed, the military now uses a single fuel – JP-8 – in its jet engines, helicopter turbine engines, and diesel engines. Diesel fuel is heavier, oilier, and evaporates much more slowly than gasoline. Because of greater use of diesel fuel across the Atlantic, European refineries are more oriented toward refining crude oil into diesel rather than gasoline, the opposite of what occurs in North America. This preference is then reflected in how fuel is marketed.
A diesel engine achieves greater miles-per-gallon than an equivalent gasoline engine. With gasoline costing up to $6 a gallon in Europe, fuel economy has historically been more important to Europeans than Americans and a key factor in their preference for diesel power, even when diesels were still noisy and dirty. Diesel fuel has a higher energy density than gasoline, with a gallon of gas containing 85 to 87 percent of the BTUs (British Thermal Units) of a gallon of diesel fuel.

Diesel engines are also more efficient than their gasoline counterparts because more power is produced as a result of the higher compression of the air/fuel mixture. Today’s gasoline engines have compression ratios of about 10:1 to 11:1, while the compression ratios in diesels can be as high as 25:1. The higher the compression ratio, the more power generated.
The much higher compression ratio means diesel engines have to be heavier and more robust. This means they are more expensive to build, but the higher cost is offset by much longer lifetimes. For instance, we’ve seen Mercedes-Benz diesels with 350,000 or more miles on the odometer running great on the original engine. Because of higher component weight and high compression ratios, diesels operate at lower rpms, producing lots of low end torque but less horsepower.

‘NEW’ DIESEL = LOWER IMPACT Environmental concerns have long impacted America’s image of diesels. Many Americans still envision a diesel-powered vehicle belching out clouds of black smoke. That’s an image we’ve seen all too often from transit buses, big-rig trucks, and older diesel passenger cars over the years But if that’s your view of diesel vehicles now, then you have a lot to learn.
Computerized, turbocharged diesel engines equipped with emission control devices have pretty much taken care of this very obvious pollution problem. If you see a modern diesel smoking, it probably can to be attributed to poor maintenance.

Besides carbon monoxide, carbon dioxide, unburned hydrocarbons, and oxides of nitrogen emissions that are common to all internal combustion engines, diesel engine designers also have to contend with significant amounts of particulate matter, or soot. Innovations such as diesel traps or diesel particulate filters are now used to mitigate this by modern diesel vehicles. Because carbon dioxide emissions are directly related to the amount of fuel consumed, the fuel-efficient diesel engine does better than its gasoline counterpart when it comes to CO2 greenhouse gas emissions.
With the growing attention being devoted to C02 reductions these days, not to mention legislation that’s sure to drive the auto industry toward much higher efficiency and lower C02-emitting vehicles, diesel is sure to have a promising future.

Source:-http://www.greencar.com/articles/clean-diesel-high-mpg-low-co2-next-big-thing.php

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