Fundamental Study on Lean Premixed Combustion under High Temperature Preheated Condition

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In order to achieve the homogeneously premixed combustion under the high temperature preheated condition, fundamental study concerning the physical process and the chemical process of combustion were examined in detail.To analyze the combustion characteristics of high temperature preheated mixture, blow-off limit was measured by using an optical burner system. The fuels used were Methane, Bethune and DME. The equivalence ratio of blow-off limit becomes lower as the preheated temperature becomes higher for all fuels. Due to the extended lean limit, combustion temperature becomes slightly lower under preheated condition, and confirmed the usefulness of the proposed combustion method. In the case of DME combustion, low temperature oxidation reaction was taking place within the pre-heater under the preheated temperature around 630 K, however it resulted in the deterioration of blow-off characteristics. On the contrary to this tendency, the low temperature oxidation reaction results in the … More promotion of ignition under the compression ignition condition.. The amount of heat release during cool flame reaction in this case was mainly affected by the oxygen concentration at the start of low temperature oxidation reaction.Low temperature oxidation mechanism taking place as a pre-combustion process in high temperature air combustion has been investigated by two methodologies. Near-infrared frequency modulation spectroscopy revealed the product formation pathways in photolytically initiated alkyl +O_2 reactions; e.g., methoxymethyl forms OH + HCHO directly and HO_2 indirectly in dimethyl ether oxidation, whereas ethyl directly forms HO_2 in ethane oxidation. In composition analysis of premixed compression ignition of dimethyl ether in a motored piston engine, significant intermediates formed at cool flames were detected. It was found that the relative amount of produced formaldehyde against residual fuel determines the extent of cool flame oxidation via the chain reaction terminating effect of formaldehyde. Less