Miniature size internal combustion (IC) engines with displacements in the neighborhood of 1 cc have the potential to function as high power and energy density miniature power supplies. The engines, which are currently used in model airplanes, have higher power and longer run times than a battery coupled to an electric motor. The Center for Compact and Efficient Fluid Power (CCEFP), a seven university research consortium in the United States, is developing miniature IC engines for applications in human size mobile devices such as robots and medical assistive devices, aiming at more compact design and longer operation time. To advance the development of new compact power supplies, it is necessary to understand the performance characteristics of current miniature engines. As the scale of an engine gets smaller, surface effects such as friction, heat loss, and leakage get more significant [ 1 ]. To measure those effects, a test bench was built for a 1.5 cc displacement AP .09 model engine. During motoring and firing tests, cylinder and crankcase pressures, engine brake torque, fuel flow rate, air flow rate and emissions were measured. From the measured data, a piston-cylinder blow-by model, suitable for miniature engines, was developed and verified. A scavenging model was developed and tuned according to experimental data. The friction was estimated by comparing indicated power calculated from in-cylinder pressure trace and brake power calculated from brake torque and speed measurements. Model engines utilize glow-ignition combustion, rather than spark ignition or fuel injection. Fuel and air are premixed and an incandescent platinum wire is used to catalyze the combustion. Combustion analysis was carried out to investigate the combustion process. A combustion model was established.