The effect of initial temperatures from about 300 degrees to 700 degrees K on the laminar burning velocity of hydrogen-air mixtures was determined from schlieren photographs of open flames. The temperature was raised in two ways: (1) by preheating of the hydrogen-air mixtures and (2) by simulated adiabatic preburning of part of the hydrogen in air at 300 degrees K so that initial temperatures of 600 degrees and 700 degrees K would be attained for the resulting mixtures of hydrogen, air, water vapor, and nitrogen. The following empirical equations for burning velocity, u, were determined: (1) For hydrogen-air mixtures, at initial temperatures with preheating T-sub-o of 287 degrees to 700 degrees K: with 29.6 percent hydrogen (stoichiometric mixture), u = 0.01011 T-sub-o to 1.271; with 45.0 percent hydrogen (maximum-burning-velocity mixture), u = 0.09908 T-sub-o to 1.413. (2) For mixtures of hydrogen, air, water vapor, and nitrogen, at initial temperatures with simulated preburning T-sub-o of 300 degrees to 700 degrees K: with 29.6 percent hydrogen (original mixture), u = 0.01145 T-sub-o to 1.695; with 45.0 percent hydrogen (original mixture), u = 0.3829 T-sub-o to 1.175. With 29.6 and 45.0 percent hydrogen (original mixture), mole-for-mole substitution of nitrogen for water vapor in the preburning experiments caused no discernible change in burning velocity.
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