Ignition Control of Mixtures in Internal Combustion Engines

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Methane would not generate cool flame during its preflame period in the autoignition processes ; quite different from the higher hydrocarbon fuels including propane, butane, gasoline and diesel oils.・ n-Butane content has more ignition promoting effect compared to ethane and propane for the methane-dominant fuel gases.・ No weighted summing rule of octane/cetane rating is approved, as suited for normal liquid hydrocarbon fuels.Measures should be found out to eliminate the fluctuation of ignition. The most important intermediate during the preflame period up to the hot-flame establishment of hydrocarbon fuels is the formaldehyde, which is closely related to the cool-flame a ppearance. We proposed herewith an ignition-control concept utilizing the gaseous formaldehyde as an additive to maintain stabilized operation of spark-ignited natural gas engines and to realize premixed compression-ignition engines (i.e.homogeneous charge compression ignition engine, HCCI). Lean fuel/air mixtures wit … More h various fuel/fuel ratios between methane and n-butane were supplied to apremixed compression-ignition engine with or without supplementary gaseous formaldehyde induction as an ignition controlling additive. The amount of formaldehyde was hundreds parts per million of total mixtures. The formaldehyde addition to the methane/butane/air mixtures has given the engine desired and stable ignition timings controllable by the amount of formaldehyde to be added, almost independent on the fuel/fuel ratios between methane and butane.A small amount of formaldehyde added into the methane/ butane/air mixtures has given the engine desired and stable ignition timings according to the amount of formaldehyde added, almost independent on the fuel/fuel ratios between methane and butane.・ The amount of formaldehyde added to the fuel/air mixture becomes a sole controlling factor to the ignition tuning. The effect of formaldehyde addition is inhibitory for the mixtures with advanced hot-flame ignition timings as contrasted with a promoting effect to the mixtures wilh retarded ignition timings.・Troubles due to the day-by-day ignition-characteristic fluctuation of the engine fuel gases can be eliminated by using a small amount of formaldehyde for the premixed compression-ignition and spark-ignited natural gas engines.・Operating range of premixed compression-ignition engine expands to both methane-abundant and butane-abundant directions.Formaldehyde is efficacious as an ignition controlling medium for the hydroribon/air mixtures in engine cylinders. The effect of formaldehyde leading to the ignition would be an inhibitory event for the cool-flame generating constituent and a promoting event of the preflame reaction of the non-cool-flame generating constituent in the fuel gases. Less