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Lean air-gas mixture combustion systems seem to be very promising solutions for IC engines in terms of lower emission indexes and higher thermal efficiency, especially in part-load operation. The main problem however is the necessity to provide the bigger activation energy for ignition of lean and very lean mixtures. In several publications and in research performed by the authors of this paper it has been confirmed, that the implementation of turbulent jet ignition (TJI) results in significantly faster inflammation of lean CNG/air mixture due to the improvement in on-ignition mechanism. The TJI-system consists of two chambers connected with nozzles. The orifices generate complex charge movement and decrease significantly the charge homogeneity in the pre-chamber, interrupting therefore first ignition process.

Direct injection into open chambers of Diesel- and S.I.- Engines is considered by the experts of automotive engineering worldwide as the best way for future economy and ecology engines [1]. Beside of the best fuel saving passenger cars driven by Diesel engines, advanced Diesel like Stratified Charge Engines as the CCSC (Controlled Combustion Stratified Charge) and the MESC (Mixture Exhaust Stratified Charge) -Engines open the way for future developments. Both engines work with the following new elements: Air assisted injection for the formation of the combustible mixture in the small cavities of prechambers, where the load control is achieved by the quantity of the injected fuel without the need of throttling the charge of the main chamber as common in today's SI engines. Pulsed Jet Combustion, where at first in small cavities of prechambers a rich mixture gets ignited.

The paper presents the thermodynamic analysis of the engine supplied with small and large diesel fuel doses while increasing natural gas quantity. The paper presents changes in the combustion process thermodynamic indexes and changes in the exhaust gas emissions for dynamically increased share of the gaseous fuel. The cylinder pressure history was subject to thermodynamic analysis, . based on which the mean indicated pressure, the heat release rate, the quantity of heat released as well as the pressure rate increase after self-ignition were determined. These parameters were also referred to the subsequent engine operation cycles by specifying the scope of the change per cycle. The relationship between the engine load and the start, the center and the end of combustion while increasing the gas amount supplied to the cylinder was indicated.

Controlled combustion in direct injection stratified charge engines can be achieved by the use of impinging jets for injection as well as for ignition, in association with a close-loop, electronic control system. Upon the description of the method of approach required for the design of a control strategy, illustrated by application to a conventional diesel engine, salient features of novel concepts for direct injection stratified charge engines are presented.