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Technology: Lean-burn catalyst offers market boon

点击量:   时间:2019-03-02 14:07:01

By PETER HADFIELD in TOKYO Mazda has developed what it says is the world’s first catalytic converter for lean-burn engines, claiming that in laboratory tests its ‘three-way’ catalyst cuts emissions of hydrocarbons, carbon monoxide and nitrogen oxides down to legislated limits. It could open up commercial markets that were previously closed by the difficulty in developing catalytic converters for such engines. Lean-burn engines were first developed in the early 1980s. They offer greater fuel efficiency than standard models because the ratio of air to fuel in the cylinder is about 50 per cent greater, and better aerodynamic flow inside it improves combustion. Three-way catalysts have been used with conventional engines, but the exhaust stream from lean-burn engines contains more oxygen, interfering with the catalyst’s reduction of nitrogen oxides. This can lead to pollution above emission limits – one of the main reasons for lean-burn engines’ lack of commercial success. In the past three years Honda, Mitsubishi and Toyota have launched lean-burn vehicles, but strict emission standards have meant that the lean-burn feature can only be used when the engine is operating at constant speeds. Sophisticated sensors are then used to select the optimum air-to-fuel ratio. Seiichi Inamoto, Mazda’s spokesman, says the company intends to launch its own lean-burn car with the new catalyst in the next two years. He says it will allow lean-burn combustion during any driving condition except full acceleration, without breaking even the strictest emission regulations. ‘Fuel efficiency is improved by 5 to 8 per cent,’ says Inamoto. Details of the new catalyst are mostly being kept secret. Mazda will say it is made of zeolite coated with precious metals, and that unlike catalysts in conventional engines, it is so efficient that no secondary catalyst will be needed to eliminate nitrogen oxides. ‘I’m quite pleased if someone really has come up with the solution,’ says Derek Charters, manager of the engine test -laboratory at MIRA, the Motor Industry Research Association in Nuneaton. ‘It puts the lean-burn engine back on the agenda.’ While the new catalyst removes one major obstacle to the use of lean-burn engines, full use will not come into effect until car manufacturers are able to increase the engine’s power performance. Japanese consumers have so far been unwilling to sacrifice performance for fuel efficiency, and presently the biggest market for lean-burn engines is in Europe. ‘I would like to see it working, to see if it’s robust,’ says Charters. ‘The outstanding questions are how quickly the catalyst heats up (to its operating temperature),