One of the possibilities to reduce diesel fuel consumption and at the same time reduce the emission of diesel engines, is the use of alternative gaseous fuels, so far most commonly used to power spark ignition engines. The presented work concerns experimental research of a dual-fuel compression-ignition (CI) engine in which diesel fuel was co-combusted with CNG (compressed natural gas). The energy share of CNG gas was varied from 0% to 95%. The study showed that increasing the share of CNG co-combusted with diesel in the CI engine increases the ignition delay of the combustible mixture and shortens the overall duration of combustion. For CNG gas shares from 0% to 45%, due to the intensification of the combustion process, it causes an increase in the maximum pressure in the cylinder, an increase in the rate of heat release and an increase in pressure rise rate. The most stable operation, similar to a conventional engine, was characterized by a diesel co-combustion engine with 30% and 45% shares of CNG gas. Increasing the CNG share from 0% to 90% increases the nitric oxide emissions of a dual-fuel engine. Compared to diesel fuel supply, co-combustion of this fuel with 30% and 45% CNG energy shares contributes to the reduction of hydrocarbon (HC) emissions, which increases after exceeding these values. Increasing the share of CNG gas co-combusted with diesel fuel, compared to the combustion of diesel fuel, reduces carbon dioxide emissions, and almost completely reduces carbon monoxide in the exhaust gas of a dual-fuel engine.
The paper presents results of co-combustion of diesel-biodiesel-ethanol fuel blend in direct injection Diesel engine. Test was performed at constant rotational speed at three commonly used loads of this engine: 100%, 85%, and 70% of load. During the test hydrated ethanol was used at a concentration of 89% of alcohol. In this study, the ethanol fuel was added to diesel-biodiesel fuel blend with concentrations up to 50% with the increment of 5%. The biodiesel was used as an additive to prevent the stratification of ethanol and diesel blends. Thermodynamic parameters of engine were analyzed, and combustion process and exhaust emission were characterized. It turned out that with the increase in engine load is possible to utilize larger ethanol fraction in blend. With the increase of ethanol fuel in blend the increase in ignition delay (38.5% for full load) was observed, but burning duration decreased (49% for full load). The ethanol fuel share in blend generally causes the increase in NO x emission (42% for full load) due to higher oxygen content and higher in-cylinder temperatures. It turned out that, at full load the unrepeatability of indicated mean effective pressure was near the same up to 50% of ethanol fuel in blend (about 2%). In case of partial load at higher ethanol fuel fraction the increase in indicated mean effective pressure un-repeatability was observed.
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