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3. Results and discussion Thermodynamic Analysis of Combustion Events in the Natural Gas Fuelled SI Engine with VVT

Table 2 3. Results and discussion Thermodynamic Analysis of Combustion Events in the Natural Gas Fuelled SI Engine with VVT

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The engine setup and valve lift profiles are shown in Fig. la.
The engine setup and valve lift profiles are shown in Fig. la.
Tab. 1. Specifications of the single cylinder Hydra engine
Tab. 1. Specifications of the single cylinder Hydra engine
Fig. 2. In-cylinder pressure vs. crank angle for selected overlaps (a), p-V diagram in log scale (b) In Fig. 2a, the in-cylinder pressure history zoomed to combustion phase is depicted. As seen, with higher overlapboth, the peak pressure and pressure at the compression stroke are lower, that is mainly due to lower amounts of gas charge filling the cylinder. Fig. 2b shows the entire p-V diagram in log scale. As observed, changes in pressure are also observed at the pumping phase with change in overlap.
Fig. 2. In-cylinder pressure vs. crank angle for selected overlaps (a), p-V diagram in log scale (b) In Fig. 2a, the in-cylinder pressure history zoomed to combustion phase is depicted. As seen, with higher overlapboth, the peak pressure and pressure at the compression stroke are lower, that is mainly due to lower amounts of gas charge filling the cylinder. Fig. 2b shows the entire p-V diagram in log scale. As observed, changes in pressure are also observed at the pumping phase with change in overlap.
Fig. 3. Locations of reference points to calculate polytropic indexes (a), exemplary distribution of compression polytropic index from selected series consisted of 300 consecutive combustion events (b)
Fig. 3. Locations of reference points to calculate polytropic indexes (a), exemplary distribution of compression polytropic index from selected series consisted of 300 consecutive combustion events (b)
Fig. 4. Polytropic indexes vs. overlap Thermodynamic Analysis of Combustion Events in the Natural Gas Fuelled SI Engine with VVT
Fig. 4. Polytropic indexes vs. overlap Thermodynamic Analysis of Combustion Events in the Natural Gas Fuelled SI Engine with VVT
Combustion phases CAO0-10 and CA10-90 can be considered as ignition delay and main combustion phase, respectively. The combustion phase CAO-10 presents itself crank angle associated with 10% heat released starting from ignition point. Hence, CA10-90 responds crank angle for 80% cumulative heat released from 10 to 90%. These combustion phases can be easily determined from cumulative heat plot O(@) (Fig. 6), which can be calculated with equation (3) by integrating equation (2):
Combustion phases CAO0-10 and CA10-90 can be considered as ignition delay and main combustion phase, respectively. The combustion phase CAO-10 presents itself crank angle associated with 10% heat released starting from ignition point. Hence, CA10-90 responds crank angle for 80% cumulative heat released from 10 to 90%. These combustion phases can be easily determined from cumulative heat plot O(@) (Fig. 6), which can be calculated with equation (3) by integrating equation (2):
Fig. 6. Cumulative heat released from combustion for three exemplary test series with various overlaps
Fig. 6. Cumulative heat released from combustion for three exemplary test series with various overlaps
Fig. 7. Combustion phases CA0-10 and CA10-90 vs. overlap (a), main combustion phase CA10-90 vs. max. HRI with variable overlap (b) As plotted in Fig. 7a, the main combustion phase CA10-90 in explicit negative trend with increase in overlap. Unlike CAO-10, this phase has its minimum at overlap nearly 60-70 CA deg. Additionally, strong negative linear correlation between CA10-90 and maximum in HRR was observed (Fig. 7b). This trend was expected to be negative, as the peak in HRR is located in the main combustion phase CA10-90.
Fig. 7. Combustion phases CA0-10 and CA10-90 vs. overlap (a), main combustion phase CA10-90 vs. max. HRI with variable overlap (b) As plotted in Fig. 7a, the main combustion phase CA10-90 in explicit negative trend with increase in overlap. Unlike CAO-10, this phase has its minimum at overlap nearly 60-70 CA deg. Additionally, strong negative linear correlation between CA10-90 and maximum in HRR was observed (Fig. 7b). This trend was expected to be negative, as the peak in HRR is located in the main combustion phase CA10-90.
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