A method of operating an internal combustion engine comprises the steps of pressurizing a liquid fuel to a pressure above 150 psig; heating the liquid fuel to a temperature above 500\xb0 F. Since this method uses the variation of impedance caused by the induction machine’s generation of field and by various shapes, the control performance is more stable than other conventional control methods. The service processing unit continues to send a service signal as a self-checking signal, and a part of the self-checking signal leaks into the radio frequency receiving unit through the duplexer. The first pair of elements is separated by at most \xbd\u03bb of the response signal. As a result, the measuring device of the present invention has the advantage of proving a simple way to measure the roundness of the cylinder. After sorting, the printed circuit boards are heated to melt the solder, and the molten solder is collected.