Diesel Engines: are they really bad for the environment?

That thick black smoke coming from the heavy truck in front of me: aren’t diesel exhaust fumes bad for the environment?

Speaking of exhaust fumes, thanks to the highly publicized event of Shintaro Ishihara, Governor of Tokyo, when he held up a bottle of diesel soot before cameras and reporters, “Diesel engines” have a negative image in Japan. But in Europe, half of new vehicles produced have diesel engines. Don’t you wonder why?

Actually, the development of clean diesel engines is making striking progress and nowadays there are less and less vehicles which produce black smoke. Diesel engines are more economical than petrol ones and emit less CO2 which is required to be reduced at the Kyoto conference. On the other hand, compared to petrol engines there was an issue of more oxides of nitrogen and particulate substance that can cause acid rain. However, this time, Honda has developed a new diesel engine with low emissions of oxides of nitrogen, at the same level as petrol ones. If this is installed in a car, diesel engines will be far better for the environment than petrol engines.

At the moment, it is only old type diesel vehicles which are the subject of regulation in the Tokyo area. Diesel engines, which were supposed to be bad for the environment, are evolving gradually, aren’t they? But I heard that in the EU emission control is getting tighter and now the USA & Japan will follow this and tighten emission control on diesel engines in the near future. Along with this movement, many car manufacturers are now using a function called “Turbo chargers” to soup up car engines. How do they work?

Turbo chargers improve heat efficiency by raising combustion efficiency, using energy from emitted gas which used to be just waste. Used especially on motorways at steady engine revs, it improves the efficiency even more. In Europe, where more and more diesel vehicles with low CO2 emission are produced, people care not only about the environment but the efficiency of diesel engines using turbo chargers.

On top of that, there is an engine called “the Stirling engine” which has now captured attention. However, this is not a new type of engine but was developed 2 centuries ago. Have you heard about it? What kind of an engine is it?

The structure is quite simple: by heating and cooling a gas at different temperatures, it is an external-combustion engine which gets power by inflating and deflating the gas inside (petrol and diesel engines are internal-combustion types). Because we can re-use waste energy effectively, this engine has now come under the spotlight again all over the world. For example, a venture capitalist and a marine company jointly started development of a Stirling engine for marine vessels in Tokyo Bay. One of the developers said, “Until now, gas emission from boats and ships at berth at Tokyo Bay was the biggest cause of air pollution. So if they can use the waste heat of the emissions to make power even just while they are there, we can get rid of a large portion of the air pollution”.

It does not sound like something they can use straight away and they will have to spend more time in developing it to improve the engine’s performance. As for diesel engines, checking old technology can be the first step towards an “Eco-friendly” society.


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