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.
Finally, the specific exhaust emissions obtained with different test cycles and according to different test procedures were compared, in order to find out not only the current pollutant emission level for small s.i. engines, but also to evaluate its sensitivity to different measuring procedures.