This paper reports a study into the fuel, economic, energy, and environmental indicators of the diesel engine operating in the diesel-gas cycle. It was established that the injection timing has a significant impact on the diesel engine indicators, in particular emissions of harmful substances with exhaust gases. The gas injection timing was investigated at crankshaft speeds n=1,300 rpm and n=1,600 rpm. At these crankshaft speeds, measurements were carried out at three different values of the injection timing. It has been determined that for each crankshaft speed of the diesel engine, the rational values of the injection timing of compressed natural gas are different. This is due to the time limits for supplying compressed natural gas to cylinders. Bench motor tests were carried out to analyze the effect of change in the gas injection timing on the diesel engine performance indicators operating in the diesel-gas cycle. The diesel engine performance indicators were also determined during a diesel cycle and during a diesel-gas cycle. The analysis has established the effect of change in the injection timing on the concentrations of carbon monoxide, hydrocarbons, nitrogen oxides, and the smoke of exhaust gases under different speed and load modes of diesel engine operation. This effect manifests itself by a slight decrease in the concentration of carbon monoxide and hydrocarbons, by the increase in the concentration of nitrogen oxides (up to 30 %), and by a significant reduction in the smoke of exhaust gases (up to 90 %). The improvement of environmental indicators of the diesel engine has been confirmed when switching its operation to the diesel-gas cycle, by 10‒16 %, with similar fuel, economic, and energy indicators. Thus, there are grounds to assert the importance of choosing and establishing the rational value for the injection timing of compressed natural gas, depending on the speed and load modes of diesel engine operating in the diesel-gas cycle.

The features of an advanced mathematical model of motion of a truck with a diesel engine operating on the diesel and diesel gas cycles are presented in the article. As a result of calculations using the mathematical model, a decrease in total mass emissions as a result of carbon monoxide emissions is observed due to a decrease in emissions of nitrogen oxides and emissions of soot in the diesel gas cycle compared to the diesel cycle. The mathematical model of a motion of a truck on a city driving cycle according to GOST 20306-90 allows to study the fuel-economic, environmental and energy indicators of a diesel and diesel gas vehicle. The results of the calculations on the mathematical model will make it possible to conclude on the feasibility of converting diesel vehicles to using compressed natural gas. Object of the study – the fuel-economic, environmental and energy performance diesel engine that runs on dual fuel system using CNG. Purpose of the study – study of changes in fuel, economic, environmental and energy performance of vehicles with diesel engines operating on diesel and diesel gas cycles, according to urban driving cycle modes. Method of the study – calculations on a mathematical model and comparison of results with road tests. Bench and road tests, results of calculations on the mathematical model of motion of a truck with diesel, working on diesel and diesel gas cycles, show the improvement of environmental performance of diesel vehicles during the converting to compressed natural gas in operation. Improvement of environmental performance is obtained mainly through the reduction of soot emissions and nitrogen oxides emissions from diesel gas cycle operations compared to diesel cycle operations. The results of the article can be used to further develop dual fuel system using CNG. Keywords: diesel engine, diesel gas engine, CNG