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In order to study the effects of air bulk motion and methane injection strategies on the development and pollutant levels of dual-fuel combustion, an intense experimental campaign was performed on a diesel common rail research engine with variable inlet configurations. Activating only the swirl or the tumble inlet valve of the engine, or both of them, it was possible to obtain, inside the cylinder, three different bulk flow structures. The air-methane mixture was obtained injecting the gaseous fuel into the inlet manifold varying its pressure and the injector position, either very close to the inlet valves, in order to obtain a stratified-like mixture, or more upstream, to obtain a homogeneous-like mixture. By combining the two different positions of the injector and the three air bulk flow structures, seven different inlet setup have been tested, at different values of engine speed and load.

In the present investigation, a parametric study of the geometric characteristics of a two-cylinder four-stroke gasoline engine was carried out. Engine power, torque, specific consumption, engine efficiency, in-cylinder pressure for both the cylinders and pressure along the intake and exhaust manifolds at different positions were experimentally measured for engine speeds ranging from 5000 to 9500 rpm. All measurements were made under steady state conditions and full load. Engine characteristics were calculated by means of a 1-D model, which was used to calculate wave propagation in the intake and exhaust manifolds. A zero dimensional model was used to account for the in-cylinder phenomena. In the 1-D model the effects of pipe curvature, restriction geometry, gas friction, and heat transfer to the manifolds walls were considered. Numerical results showed good agreement with the measurements over the investigated range of operating conditions.