The Study of Possibilities for Reducing Fuel Consumption for Natural Gas Engine Based on Diesel at Idle Speed

Abstract

Diesel-to-natural gas engine conversion is an important economic task. In this modification the gas engine has some fundamental differences from the diesel: forced ignition is replaced by Compression ignition; as a rule, external mixture formation instead internal mixture formation; the quantitative load control using throttle - instead quality load control. The latter is one of the main reasons for the deterioration of the fuel economy of the gas engine especially at low loads, because of the significant increase in pumping losses when reducing the load by throttling. The greatest value of such losses is on the idle speed. The authors considered the possibility of increasing the efficiency of the gas modification due to the implementation of the Miller cycle, where the load reduction is achieved by variable valve timing - mainly the valve Duration and intake valve closing angle. In this case, the load reduction is achieved without the use of throttling the fuel / air mixture. The analysis is performed using a calculation method, which was developed a special program takes into account the main physical processes of the gas engine at low operating conditions. The authors considered several options for improving fuel economy at engine low load operation for the engine KAMAZ-820.74-300, including the possibility of using lean air fuel mixture, increasing the compression ratio, load management using changing valve timing. The authors defined the values of temperature and pressure at characteristic points of the pressure volume diagram, and the values of indicated thermal efficiency of an engine, fuel consumption and other parameters for the five variants of idling. The authors presented the calculated pressure volume diagrams of a Miller cycle at idle. The authors have shown the best option, where possible fuel economy improvement at idle is 25 % compared to the base engine.