The invention relates to an external
combustion type engine and a working principle thereof. The external
combustion type engine comprises a compressing cooling part, a heating expanding part, a heat regenerator and a burner. The external
combustion type engine is characterized in that the compressing cooling part comprises at least two
double acting compressors connected in a series connection mode, one cooler is arranged between every two adjacent compressors, the expanding part comprises at least two
double acting expansion machines connected in a series connection mode, the front of an air inlet of every expansion
machine is connected with a heater, the compressing cooling part and the heating expanding part are connected with the heat regenerator, and a burner inlet is communicated with an exhaust port of the last stage of expansion
machine. The working principle is that after air is subjected to multistage compression intercooling, backheating heat absorption, multistage heating expansion and exhaust combustion, gas servers as a heat source of the heater and the heat regenerator. The external combustion type engine has the advantages of being high in
thermal efficiency, good in fuel adaptability and small in
pollution and running stably and is suitable for improvement of similar products.