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An experimental investigation was carried out in order to point out the state of the art of the exhaust emissions of small spark ignition engines for non-road mobile machinery. 14 different engines from different manufacturers, with rated power below 18 kW, were selected as representative of the most common non-road mobile machinery, including lawn mowers, chain saws, trimmers, snow-removal equipments and portable gensets: 10 engines were 4-stroke (one of which also equipped with a three-way catalyst), while 4 were 2-stroke (three of which equipped with an oxidation catalyst). After a run-in period, exhaust emissions were measured according to different test cycles: moreover, an endurance run test of 100 hours was also performed for 5 engines.

In order to evaluate the genotoxic potential of DI diesel engine exhaust, Ames tests based on TA98 and TA100 bacteria strains have been conducted. The presence of nitro- and dinitropyrene was proved by comparison of TA98 to TA98NR and TA98 1,8DNP6, respectively. One light and three heavy duty diesel engines, representing past, present and future production, have been tested under steady-state and transient operating conditions. A correlation between engine load and mutagenic activity has been shown from the particulate extract. Water port injection reveals a dramatic decrease of mutagenicity at high load conditions. In the particulate extract from future very low NOx engines, no nitro- and dinitropyrenes are detected. Engines representing past and present technology however, contain these highly mutagenic compounds. High quality diesel fuel yields another substantial decrease of mutagenicity.

A small displacement direct injection diesel engine family is being developed to improve thermal efficiency as compared to the IDI version. 4- and 6-cylinder in-line engines of 2.5 and 3.7 liters displacement, both naturally aspirated and turbocharged are designed. Fuel economy of these direct injection engines is compared with the corresponding indirect injection diesel engine family at the same level of performance. It appears that with direct injection good fuel economy is achieved. However, emission constraints have to be taken into account. For different applications compromises between fuel economy and emissions complying with government regulations have to be found.