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Nowadays the main part of investigations in controlled auto-ignition (CAI) engines are centered on performance or some engine processes simulation, leaving aside particle number (PN) emission. The present work is focused on this last topic: PN emission analysis using two different injectors in a 2-stroke CAI engine, and a global comparison of PN emission of this engine with its homonymous 4-stroke engines at two operating conditions. The study was performed in a single-cylinder gasoline engine with 0.3 l displacement, equipped with an air-assisted direct-injection (DI) fuel injection system. Concerning the injectors evaluated, significant differences in PN emission have been found. When the I160X injector (narrow spray angle) was used, PN emissions were reduced. The spray cone angle during the injection event appears to be a key factor for PN emission reduction.

In the present paper, the use of a 2-stroke (2S) concept in an automotive gasoline engine is evaluated. In a first stage, the engine architecture chosen is discussed. Taking into account the requirements in gas exchange processes, a uniflow scavenging design was retained (intake ports in the cylinder, controlled by the piston; exhaust valves in the cylinder head, controlled by a Variable Valve Timing, VVT, system), performed by an external blower driven by the crankshaft. To avoid any fuel short-circuiting and to keep an acceptable cost, a direct injection (DI) air-assisted fuel injection system was selected. Since the engine behavior is much more complex compared to a classical 4-stroke engine, some complexity in the engine design needs to be added to allow engine optimization at the different operating conditions. This is the main reason why a VVT system, as well as a flexible fuel injection system were selected. In a second stage, the chosen engine concept is evaluated.