In general, spark ignition is not practical in smaller engines (0.6 cubic inches and smaller). It can be done, in fact it was done in the 1940's before Mr. Arden invented the glow plug. The 1/4 x 32 glow plug thread size was originally the size of micro spark plugs used in these engines. The problem is that an ignition system for a small engine is just as heavy as one for a big engine.
Even though glow fuel is expensive, a .40 size engine does not burn much of it.