<div class="htmlview paragraph">In the present work it is proposed to improve the efficiency of an Otto engine by development of a system with assisted catalytic ignition and combustion. The system is characterized by the use of a lean mixture in a swirling charge, substantial increase of the compression ratio, and application of a catalytic prechamber. For a long time, the combustion of lean mixtures has been one of the most important tendencies in development of gasoline engines. To be able to burn lean mixture at full load it is necessary to induce intense swirl in the combustion chamber and to increase compression ratio. One of the possible ways to burn lean homogeneous mixture is to use the combustion system made up of a main combustion chamber and prechamber. The latter is fed with the same lean homogenous mixture as the main combustion chamber, but it contains catalytic insert, kept at temperatures high enough, to secure catalytic reactions and torch ignition of the main charge. The combustion system was applied to four cylinder Diesel engine Ford FSD 425, with 2.5 l capacity, modified to the Otto cycle. Fuel injectors in the original engine were replaced with small prechambers. Each prechamber was equipped with catalytic insert and spark plug. The geometric compression ratio of the modified engine was ε = 16. A high swirling ratio was preserved from the original engine. After preliminary tests and series of succeeding improvements the engine started to work in optimum conditions. The modified Otto engine reached the original level of power 46,5 kW, at 4000 RPM., and original specific fuel consumption 254 g/kWh, at 2100 RPM. It worked more than 300 h. A small prechamber with the catalytic insert attached to the engine structure improved considerably the combustion characteristics, thus making possible operation with lean mixtures, at high compression ratio and high efficiency. It was found in experiments that catalytic ignition either can accompany spark ignition or it can be used as independent source of ignition. In both cases it increases the fuel economy and reduces emission of CO, HC and NO_x, in comparison with pure spark ignition.</div>