Hi Tom and Colleagues, Tom as you are clearly the authority on what you say:
Simple thermodynamics predicts and practice shows that both power and efficiency increase linearly with CR. Since producer gas has an octane over 180, various groups have been "souping up " gas engines, using CR in excess of 18/1. Little old producer gas has grown up. I would be pleased to have explained from anyone with producer analysis gas experience, how you can say that all producer gas is over 180 octane, or possibly "can" be over 180? It would be difficult to convince the engine expertise on whom I rely, to accept that all producer gas has the same degree of anti-knock, given not all gasifiers are equal. Based on 135 btu/ft3, the Caltex Oil Co. guy who advised us regarding octane rating, "suggested" we stick to 120 as the maximum, being a realistic figure. I think it important to clarify how variations of producer gas octane can eventuate. This then leads to a second question, which personally creates a black hole in how I have been forced to accept the reality, of working with high compressions in diesels operating on dual fuel/producer gas. How can then, the spontaneous ignition temperature be increased more than the "about" 600C found at 16:1 ratios, given that we also must consider the operating temperatures? I can appreciate that you can tweak any engine performance in a fixed load/conditions situation, but I doubt if combustion stability at over 17:1 could be assured if the load/conditions fluctuate as for variable power generation. In the Lister (NZ) workshops, we did many controlled trials with their larger engines (16:1), but one sticks out, because it frightened us all when it happened. We had finished a long full load test without the air filter fitted, and when we dropped the load from the hot engine, I put the air filter back on, which immediately began to wind the rpm up well over the 1,500 of the diesel governor setting. It was a run-away situation on auto ignition, because locking out the diesel had no effect. It was fixed by pulling off the flexible gas connection. Clearly change of the gas/air mix affects this spontaneous ignition temperature, and there would seem to be little value of working with ratios over 16:1 unless it can be proved the economics or emissions can be seriously advantaged. It does come down to $$$ in the end(:-) Not sure if I can locate some of the peak pressure charts from that time, but certainly Prof.John Stevenson of Auckland University's Mechanical Engineering was involved, and used them in a Paper he presented on how he thought dual fuelled diesels should be controlled. Enlightenment anyone please? Doug Williams. Fluidyne.
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