Fig. 12 Comparison of ignition delay predicted with ignition delay measured (Air, n=800〜2000rpm)
Figures 11(a)〜(d) show the comparison of the ignition delay predicted in this way with the data measured. The predicted values seem to have good correlations with the measured ones for the mixtures of air-methane, air-propane air-hydrogen mixtures and only air. Even when the engine speed was changed between 800 and 2000 rpm for the normal operation, the ignition delay predicted have a very good correlation with the measured values as shown in Fig. 12.
5. CONCLUSIONS
Gaseous fuel of methane, propane or hydrogen was induced from intake port and light oil was injected in the cylinder. Ignition delay was investigated and the concept of Livengood-Wu's equation was discussed. Main results obtained here are summarized as follows:
(1) The concept of Livengood-Wu can be applied to the combustion in dual fuel engines by changing the value of a constant, A.
(2) When methane or propane is mixed with intake air, the ignition delay becomes long because the temperature of compressed gas decreases due to the decrease in the ratio of specific heats. When hydrogen is mixed with air, the ignition delay becomes large because the molar concentration of oxygen decreases.
(3) In these kinds of dual fuel engine, oxidation of the mixture can be observed near the TDC of compression at the injection timing is retarded. And the fluctuation of the ignition timing occurs due to the oxidation of the mixture near the TDC.
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