THERMODYNAMIC ANALYSIS OF COMBUSTION EVENTS

The main aim of the research was to investigate influence of overlap of the natural gas fuelled spark ignited

engine on the following parameters: Indicated Mean Effective Pressure (IMEP), heat rate release including

combustion phases (ignition lag, main combustion phase). The content of the study includes results from processing

in-cylinder pressure measurements, heat release rate analysis, combustion phases, and finally the conclusions. The

tests were carried out on the test bed including the single cylinder research engine with a displacement volume of

550 cm3. The engine was equipped with independent cam phasors for both intake and exhaust valves, but for this

investigation, the exhaust valve timing was fixed (the exhaust cam centre line was fixed at -95 crank angle (CA) deg

before Top Dead Centre) and intake valve timing was changed (the intake cam centre line was varied from 90 to 150

CA deg after Top Dead Centre). The overlap was changed in the range from 85 to 25 CA deg. 8 tests series were

performed, each singular series consisted of 300 consecutive engine combustion cycles. As observed, by varying the

valve overlap it contributes to significant change in the peak combustion pressure, peak of heat release rate, and

combustion phases. Summing up, variable valve timing affects compression and expansion strokes by changing

polytropic indexes due to various amounts of exhaust residuals trapped in the cylinder. It affects not only engine

volumetric efficiency but also the heat release rate and IMEP, so it does engine performance. Thus, variable valve

timing can be considered as valuable tool that can be applied to the natural gas fuelled internal combustion engine.