Paper 13: Exhaust Emissions of Vehicles Tested to the Draft European Procedure

The work in this report was prompted by the probability of legislation in most European countries to limit the emission of carbon monoxide and possibly unburnt hydrocarbons from the exhausts of petrol-engined vehicles. A draft method of testing has already been agreed upon and this work was carried out in accordance with this draft procedure. The object of the work was to establish the baseline emissions of vehicles currently in service in Great Britain and, to achieve this, approximately 100 cars, representative of the age and engine capacity distribution of the population of Great Britain, were tested. The full test procedure consists of four cycles of a specified speed–time relationship driven from cold in which the exhaust gas is collected in bags for subsequent measurement of gas volume and carbon monoxide and hydrocarbon concentrations. For greater convenience, most tests were run from the hot condition and corrections applied to give the equivalent cold start data. These corrections, obtained by comparison of emissions from hot and cold start tests, were factors of 1·05 for mass and 0·95 for concentration. The results of tests indicated that the average emission of carbon monoxide for cars in service in Great Britain is 172 g for the four cycles of the test procedure from a cold start, which is equivalent to a concentration of 3·4 per cent; the range of emissions is from 0·60 to 7·36 per cent. Although considered of less importance in Europe, hydrocarbons were also measured and gave an average emission of 11·0 g from a cold start. Simple engine maintenance, such as corrections of ignition faults and carburettor maladjustments, was carried out on about half of the vehicles tested; these vehicles were representative of the sample as a whole and the maintenance resulted in a 20 per cent reduction in average carbon monoxide mass emissions and 10 per cent reduction in average hydrocarbon emissions. Idle emission measurements were carried out with the vehicles hot. These varied from 0·2 to over 11·6 per cent carbon monoxide, with an average level of 6·1 per cent. The average hydrocarbon emission was 1550 p.p.m. Engine tuning reduced the average idle carbon monoxide and hydrocarbon emissions by 29 and 40 per cent respectively. The idle setting was found to have a marked effect on emissions over the cycle, probably because of the large percentage of time in the cycle which is at very light throttle opening or closed. Some comparisons were also made between the results in relation to the U.S. Federal and proposed European test methods, but results were too scattered to warrant firm conclusions.