Experimental study the impacts of the key operating and design parameters on the cycle-to-cycle variations of the natural gas SI engine

High cycle-to-cycle variations (CCV) in the spark ignition (SI) engine will not only lead to incomplete combustion and even misfire, but also affect the fuel economy and even influence the drivability and conformability of a vehicle, particularly at the lean-burn condition. However, the detail information about the root causes of CCV are still relatively limited, particularly the natural gas SI engine. In this paper, the impacts of the key operating and design parameters were investigated on the CCV of the high compression ratio SI natural gas engine under lean mixture condition. The results indicated that the in-cylinder pressure distribution tended to be concentrated, the number of partial burning or incomplete combustion cycles also reduced with increasing the engine speed. With increasing the load, the in-cylinder pressure distribution, peak combustion pressure and its location were tended to be concentrated. Furthermore, the number of the partial combustion or post combustion cycles declined from low-load to medium- and high-load zones. Moreover, the relationship between the peak combustion pressure and its location was almost linear with increasing the engine load. Unfortunately, with further increasing engine load, in-cylinder pressure traces started to disperse slightly. Under the low-load condition, in-cylinder pressure traces were tended to be concentrated with increasing compression ratio (CR). As CR continually increased, its influence on the in-cylinder pressure distribution decreased. In addition, the number of the partial combustion or post combustion cycles decreased with increasing CR. However, under the high-load condition, increasing the CR has slightly effects on the in-cylinder pressure distribution.

Automated summary

This study investigated the impacts of key operating and design parameters on the cycle-to-cycle variations in a high compression ratio SI natural gas engine under lean mixture conditions. The results showed that with increasing engine speed, there were fewer incomplete combustion cycles and the in-cylinder pressure distribution became more concentrated. Increasing load led to more concentrated pressure distribution and peak combustion pressure. Additionally, the relationship between peak combustion pressure and load was nearly linear, but increasing load caused the in-cylinder pressure traces to disperse slightly. Under low-load conditions, increasing compression ratio led to more concentrated pressure traces and fewer incomplete combustion cycles, while the effects were slight under high-load conditions.