Rotary valve technology can provide increased flow area and higher discharge coefficients than conventional poppet valves for internal combustion engines. This increase in intake charging efficiency can improve the power density of four-stroke internal combustion engines, particularly at high engine speeds, where flow is choked through conventional poppet valves.
In this work, the valvetrain of a light duty single cylinder spark ignition engine was replaced with a rotary valve train. The impact of this valvetrain conversion on performance and emissions was evaluated by comparing spark timing sweeps with lambda ranging from 0.8 to 1.1 at wide open throttle. The results indicated that the rotary valvetrain increased the amount of air trapped at intake valve closing and resulted in a significantly faster burn duration than the conventional valvetrain. Additionally, the spark to CA10 burn duration of the rotary valvetrain was highly sensitive to spark timing, which was not true of the baseline engine, nor is it true of conventional spark ignition engines in general.
The explanation behind this rapid combustion and high combustion duration sensitivity to spark time is related to the large amount of tumble induced by the flow through the rotary valve, which is unabated axially downward unlike with a poppet valve. Thus, the rotary valve showed not only improved power density, but more rapid combustion. However, the rotary valve does introduce channels which appear to have negatively impacted unburned hydrocarbon emissions. To complete the study, a load sweep was performed at 3300 rpm, demonstrating that there was a slight brake specific NOx benefit to the rotary valvetrain despite producing higher unburned hydrocarbons, particularly at part load operation.