Catalytic reaction is not required but it does allow engines to operate at rpms lower than max. The first glow plug/engine was an ignition Bantam .19 using a standard spark plug whose electrodes had been filed down until they were very thin. The fuel content was a closely guarded secret but I feel certain that it was probably a very high nitro content. It was called Liquid Dynamite and it had a fruity banana odor. Artie Hasselback, Bronx, NY) developed the fuel and he called his speed job "Miss Liquid Dynamite.". He demonstrated his Class A U-Control speed job to some local clubs and fellow U-Control types at an armory in the Bronx. The battery, coil, and condenser were in a pack outside the airplane. Artie started the engine (by hand) leaned it until it was screaming for mercy (probably 25-30K rpm), let it run for a short time to thoroughly heat the plug until it would glow then he pulled the high tension lead off the engine. Lo and behold the engine kept running without missing a beat. I know because I was there. It had to be 1946 -47 or thereabouts because I was still in high school. and flew with a club called the Westchester Aeronuts. I recall flying both Class A and class C speed using a Bantam 19 and a McCoy 60 (later stepped up to a Hornet
60) using the filed down plug spark plug, external ignition pack and Liquid Dynamite fuel. The engine either ran or it didn't depending on how you filed the plug. Too thin and it wouldn't last for TO, too thick and it would stop as soon as the high tension lead was disconnected. Back in those days the old timers were in their 20's or 30s and I never met one who wasn't enthusiastic about helping a kid with stars in his eyes and dreams of flying high enough to touch the clouds.That's my story and I'm stickin' to it :-) BTW, soon after the demo a fuel was developed that had a distinctive fruity odor attributable to the fact that it contained organic (?) esters.