The average time a city bus spent at idle and at various speeds over its operating range was determined from the tachographs of public service vehicles on routes in Central London. These data were used to construct a test cycle which reflected those driving patterns. A London Buses Leyland Titan bus was fully instrumented to measure gaseous and particulate exhaust emissions and then driven to the cycle on a test track at the Transport and Road Research Laboratory. The vehicle was subsequently driven on the road to simulated in-service conditions. From the point of exhaust emissions, the cycle was less severe than the simulated in-service results. A comparison of results from the cycle to ECE R49 values for the same engine type was made by calculating emission values in terms of grammes of pollutant per kilogram of fuel used. This showed the R49 result underestimated carbon monoxide, hydrocarbon and oxides of nitrogen. Levels of particulate emissions gave lower values over the R49 test than those obtained from the test track. The main reason for the differences appears to be the weighting factors applied to the R49 results, these reflect truck on motorway operation, which is different from buses operating in city centre traffic. (A)
Samenvatting