Internal Combustion Engines

The internal combustion engine is often held up as one of the chief curses of our times, mainly because of the emission of noxious gases, but also due to noise, personal injury and other more esoteric issues. It seems unlikely that the internal combustion engine will be legislated out of existence, but the quality of the engineering research required to meet the ever more stringent legislation, while delivering a competitive product is very high indeed.

In the IC engine group, there are several inter-related activities:

Measurement and control of pollution

IC engines are by law required, in developed countries, to emit exhaust gases which contain very low levels of particulate matter, carbon monoxide, unburnt fuel, and oxides of nitrogen. The latter two, in the presence of sunlight, are responsible for photochemical smog: only occasionally is this a problem in the UK (not just because of the lack of sun - still air conditions for longish periods are also required, as the smog develops over periods of hours and days). Places such as Athens, Mexico City and Los Angeles are badly affected, although other European cities have sometimes had to issue directives banning road traffic for extended periods due to smog exceedances. Carbon monoxide is, of course, poisonous.

Under conditions of good engine design and control, exhaust after-treatment catalysts enable very low levels of emission into the environment to be achieved. Current legislation limits the exhaust levels to a certain mass of particulate matter, but recent research indicates that it may be the number, rather than the mass of particles, which is related to health effects. If this proves to be the case, a great deal of work, some of it already underway at Cambridge, will be required to assess measurement methods and IC engine emission characteristics anew. For example, the gasoline (petrol) engine may need to be re-examined as a significant particle emitter, especially in its direct injection form - at present the Diesel engine is usually regarded as the only serious IC particle producer.

We have been involved in the development of a series of very high performance emissions measurement systems, in particular, those with high frequency response, which have resulted in commercial devices, now marketed world-wide. New work is underway on sensors to measure particulates from IC engines.

The way in which an engine is controlled (air/fuel ratio, timing (either spark and/or injection), valve timing, etc., determines the emissions levels. Poor control will result inevitably in either emissions increases or poor driveability or both.

Exhaust After-treatment Modelling

Apart from transporting the exhaust gas to the rear of the vehicle, and reducing the noise levels to acceptable standards, the exhaust system of current gasoline vehicles (and an increasingly higher proportion of diesel-engine vehicles) houses a catalyst, which for the catalysts most often used at present, will only work when between certain temperatures (less than 300^oC and it is inactive, above 900^oC it is damaged). The catalyst must therefore be placed where it will heat up quickly, whilst never becoming so hot that it becomes damaged. The thermal and chemical processes occurring within the catalyst are very complicated indeed. Improving our understanding of the heat transfer processes in the exhaust system leading to the catalyst, and the exact mechanisms of pollution conversion to benign products within the catalyst is therefore of importance. Work in this area is conducted in collaboration with members of the Chemistry Department (C). People: Professor Nick Collings, Dr Richard Lambert (C), Professor Keith Glover, Dr Krishnan Balakrishnan (C), Steve Cornelius.

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