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Measurement procedures for the legal limitation of emissions from heavy duty engines should adequately reflect the actual use of such engines in practice. Equally important is the possibility to monitor the emision performance of certified engines on the market. This paper gives a short overview of the experiences with the Dutch in-use compliance program for HD vehicles. The results indicate that such a monitoring of the existing fleet is of great importance for the national authorities. This means that any measurement procedure envisaged for legislation purposes should take account of the requirement of relatively easy monitoring of the emission behaviour in service just as much as the requirement of adequate simulation of practical vehicle operation.

The closed-loop threeway catalyst on the European market has considerably reduced the emissions of passenger cars in an absolute sense. The question arose if gaseous fuels still have a real advantage. To answer this question an extensive programme was set up to compare gasoline and diesel with LPG and natural gas. Not only the regulated components, but also a whole range of unregulated components were measured. The resulting data were grouped into environmental aspects, such as direct local toxicity, longterm toxicity, smog, acidification and global warming. The conclusion is that gaseous fuels still hold an advantage over liquid fuels.

The definition of what is likely to be the new EEC extra-urban cycle has made it possible to determine the emission characteristics of cars fitted with different emissions control equipment. Central part of the evaluation programme were three versions of experimental lean and dilute burn engines in comparison with engine modifications and open and closed loop three-way catalyst systems. It is concluded that both lean or dilute burn plus an oxidation catalyst and the closed loop threeway catalyst can lead to sizeable reduction of emissions. The former being clearly superior in CO-emissions, the latter holding this position in NOx-emissions. It is speculated that the ultimate clean gasoline engine is to be composed of the two systems.

Urban buses are logical candidates for catalytic trap oxidisers (CTO's). Smoke and particulates present more acute problems in an inner city environment than on open roads, while on the other hand urban bus operation gives better chances of succesful regular regeneration than long-distance truck operation. With the support of the Dutch Ministry for Environmental Protection two CTO's are tested in urban bus operation in the city of Rotterdam. The program comprises extensive mapping of the exhaust gas quality at the start (gaseous emissions, smoke, particulates, sulfate and aldehydes) and regular monitoring of durability aspects at 30,000 km intervals. This paper presents the results of the first evaluation.

In a vehicle demonstration programme the high compression lean burn technology showed good potential for further improving emissions and energy effiency of the average European car. At the US ‘83 emission control level a 10 per cent improvement in fuel consumption over the equivalent presentday vehicle was found under European city and highway driving conditions. An oxidation catalyst was found an essential and effective element of the set-up. Special attention should be paid to the representation of actual driving patterns in Europe in relation to the type approval test procedures. Especially for control of NOx emissions the situation is very unsatisfactory. Suggestions for improvement are made.