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To downsize a spark ignited (SI) internal combustion engine (ICE), keeping suitable power levels, the application of turbocharging is mandatory. The possibility to couple an electric drive to the turbocharger (electric turbo compound, ETC) can be considered, as demonstrated by a number of studies and the current application in the F1 Championship, since it allows to extend the boost region to the lowest ICE rotational speeds and to reduce the turbo lag. As well, some recovery of the exhaust gas residual energy to produce electrical energy is possible. The present paper shows the first numerical results of a research program under way in collaboration between the Universities of Pisa and Genoa. The study is focused on the evaluation of the benefits resulting from the application of ETC to a twin-cylinder small SI engine (900 cm3).

Storing hydrogen is one of the major problems concerning its utilization on board vehicles. Today hydrogen can be compressed and stored at 200 or 350 bar (it is foreseen that in a near future storage pressure will reach 700 bar, according to new expected regulations and using tanks in composite materials) or cryogenically liquefied. An alternative solution is storing hydrogen in the form of ammonia that is liquid at roughly 9 bar at environmental temperature and therefore involves relatively small masses and volumes and requires light and low-cost tanks. Moreover, ammonia contains almost 18% hydrogen by mass and, by volume, liquid ammonia contains 1.7 times as much hydrogen as liquid hydrogen. It is well known that ammonia can be burned directly in I.C. engines, however a combustion promoter is necessary to support combustion especially in the case of high-speed S.I. engines.

Direct fuel injection is becoming mandatory in two-stroke S.I. engines, since it prevents one of the major problems of these engines, that is fuel loss from the exhaust port. Another important problem is combustion irregularity at light loads, due to excessive presence of residual gas in the charge, and can be solved by charge stratification. High-pressure liquid fuel injection is able to control the mixing process inside the cylinder for getting either stratified charge at partial loads or quasi-stoichiometric conditions, as it is required at full load. This paper shows the development of this solution for a small engine for moped and light scooter, using numeric and experimental tools. In order to obtain the best charge characteristics at every load and engine speed, different combustion chambers have been conceived and studied, examining the effects of combustion chamber geometry, together with injector position and injection timing