Research on the combustion and emission characteristics of homogeneous dual cylinder free piston generator by ignition strategy

As a kind of new technology able to replace traditional power sources the dual cylinder free piston generator possesses the features of variable compression ratio, modularization, high thermal efficiency, and low emission, and has become the focus of academic circles in recent years. However, the power and emission performance are seriously affected by the fluctuation of working condition parameters in the combustion process. As such, the key factors affecting the combustion and emission characteristics of the generator were explored in the present study through a combination of experiment and simulation. The results reveal that, unlike traditional internal combustion engines, a richer mixture did not improve the combustion quality of the generator, but could significantly reduce NOx and SOOT emissions. At the same time, the lean mixture could significantly reduce the combustion quality and increase SOOT emissions, but could still reduce NOx emissions. To be specific, when the equivalence ratio varied from 1.0 to 1.2 and the ignition time was gradually increased from 10 degrees ECA BTDC to 24 degrees ECA BTDC, the indicated thermal efficiency only fluctuated within a small range of 1.8%-2.3%. On the contrary, the NOx and SOOT emissions decreased by at least 89.0% and 72.8%, respectively. Further, when the equivalence ratio variation range was 0.8-1.0 and the ignition time was gradually increased from 10 degrees ECA BTDC to 24 degrees ECA BTDC, the indicated thermal efficiency decreased by 43.9%-117.4% and the NOx emissions decreased by at least 48.7%, while the soot emissions increased by 67.7%. Additionally, at the ignition time of 24 degrees ECA BTDC with the equivalence ratio1.2, the generator achieved lower NOx and soot emissions and up to 33% indicated thermal efficiency in related research cases.