European car makers regard diesel as a strong force in the foreseeable future. Compared with petrol engines, diesel engines inherently use less fuel and therefore emit less greenhouse gas - CO2.
NOx and CO level are also lower.
Unlike petrol engines, diesel engines don’t need an ignition system. Due to the inherent properties of diesel, combustion will be automatically effective under a certain pressure and temperature combinations during the compression phase of Otto cycle. Normally this requires a high compression ratio of around 22 : 1 for normally aspirated engines. A strong thus heavy block and head is required to cope with the pressure. Therefore diesel engines are always much heavier than petrol equivalent.
The lack of ignition system simplifies repair and maintenance, the absence of a throttle also helps. The output of a diesel engine is controlled simply by the amount of fuel injected, this makes the injection system very decisive to fuel economy.
Common rail direct injection systems, gifted by their high-pressure, precise injection, improves fuel efficiency a lot.
Even without direct injection, diesel inherently delivers superior fuel economy because of leaner mixture of fuel and air. Unlike petrol, it can combust under a very lean mixture. This inevitably reduces power output (no free lunch !), but under light or partial loads where we don’t need so much power, its superior fuel economy shines.
Part of the explanation for the inferior power output is the extra high compression ratio. On one hand the high pressure and the heavy pistons prevent it from revving as high as petrol engine (most diesel engine deliver peak power at lower than 4500 rpm.), and the long stroke dimension required by high compression ratios favours torque instead of power. This is why diesel engines always low on power but strong on torque. Combine these with the lower level of combustablility and stored energy of Diesel fuel and you get a hard working slug.
To solve this problem, diesel
makers prefer to add turbocharger. A Turbo’s top end power suits the torque
curve of diesel. Therefore today’s turbo diesel
outputs similar power to a conventianally aspirated petrol engine with similar capacity, while
delivering superior low end and mid range torque and fuel economy. For instance
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As emission regulations keep tightening in Europe, diesel technology is progressing and catching up petrol, European car makers produce more and more diesel engines.
Today diesel consists of 1/4 to 1/3 cars sold in Europe.
Some countries like France and Italy the percentage is even up to 40%.
In Germany, Mercedes’ engineers expressed their worries about the tightening of emission regulations in the future which may eventually kill all large capacity petrol engines,
They believe diesel is the only way to pass the requirements. Not only Stuttgart, but BMW and Audi have also developed their first-ever powerful turbo diesel V8s for fitting in their flagship models.
Diesel technology is taking off. The last problem to be cleared is the excessive particles emitted, which is mostly carbon or large hydrocarbon particles which are claimed to be contributing to smog and dark smoke. PSA has developed an Exhaust particle filter and will be equipping its HDi common-rail series in year 2000.
In the US, where petrol is cheaper than bottled water, virtually no one is producing diesel cars. Instead, they put their bet on fuel cell technology. (Ford will put fuel car cars into mass production in 2004) However, most experts agree that fuel cell won’t be able to replace conventional combustion engines in the foreseeable future. Technology breakthrough in fuel cells will not come as big or as quick or as cheap as diesel.
In Britain the Government has decided that it knows better than the Engineers from all the major European manufactures and taxes Diesel to a punitive level. Bending its own Road fund license scheme to favor petrol's. Many of the more advanced Diesels in larger more expensive classes of vehicles will probably never be seen in Britain.