抄録
Formaldehyde artificially added into the mixtures is efficacious as an ignition control medium for hydrocarbon fuels in engine cylinders. The vapor added into the mixtures has given the premixed compression-ignition (HCCI) engine a stable ignition timing, which is controllable to get the MET by the amount of formaldehyde to be added. The effect of formaldehyde addition is either suppressing or promoting. A universal criterion of the formaldehyde effect resulting whether in the advanced or in the retarded hot-flame appearance from the original ignition events has been elucidated through experiments over a wide range of parameters on the fuel octane or butane rating, the equivalence ratio of the mixture, and the mixture temperature to be raised. The formaldehyde would be a suppressing additive under the cool-flame generating constituents, temperature and pressure conditions, and a promoting additive under the poor cool-flame generating conditions in the cylinder charge during the preflame reactions leading to the ignition. The added formaldehyde is superfluous to the ignition event originally belonging to the cool-flame dominant regime, which would give a suppressing effect. On the other hand, the artificially added formaldehyde could be a starting point of preflame reactions leading to the final hot ignition belonging to the blue-flame-dominant regime, where a few fuel transition and low intermediates appear, and where the high temperature chemistry dominates. It allows a short cut of the preflame induction period, in consequence, a promoting effect for the ignition. The low-temperature-ignition classification; three typical regime, "cool-flame dominant regime", "negative-temperature-coefficient regime" and "blue-flame dominant regime" would be a universal advanced/retarded criterion on ignition of fuel/air mixtures with formaldehyde doping for the ignition timing control in the piston compression engines.
