نشریه تحقیقات موتور
پیاپی 35 (تابستان 1393)

Homogenous charge combustion ignition (HCCI) is an excellent method for higher efficiency and to reduce NOx and particulate matter simultaneously in comparison to conventional internal combustion engines. However، reaching for higher loads and improving combustion phasing control are important challenges for the HCCI research. In this study، thermal stratification using variable intake charge temperature، the EGR ratio and variable glow plug temperature have been investigated. A combination of experiments on single cylinder engine and the 3D simulation of combustion was used for this work. As a result، increasing intake charge and glow plug temperature advanced combustion timing، shortened ignition delay time and decreased the rate of heat release. Higher combustion efficiency and higher the allowable engine load could be obtained by the increase in the rate of EGR. In general، thermal stratification has the potential to extend high-load limits of HCCI combustion by improving the control over the combustion phase; as well as reducing the maximum rate of pressure rise.

Depleting petroleum resources، increasing costs، and requirements of energy security، have led to an increase interests in renewable fuels، in recent years. Among various alternative fuels، biodiesel and dimethyl ether (DME) fuels are the most popular. In this paper، spray characteristics of diesel and those two fuels have been studied numerically under different physical conditions via the AVL-FIRE software. Injection pressure was kept constant in 50 and 100 MPa and two different pressures were considered for ambient pressure; 1 and 2 MPa. The results were in a good agreement with experimental studies. Spray characteristics such as tip penetration، Sauter mean diameter (SMD) were analyzed. Results showed that in the same physical conditions، DME had the smallest value for spray penetration and diesel had the largest values. In addition، in the case of two different ambient and injection pressures، biodiesel had the largest SMD value and DME has the smallest value in comparison to two other fuels، which means better atomization of DME at same injection and ambient conditions. The spray tip penetration was influenced by ambient pressure in each studying fuels; decreased as the ambient pressure increased، and SMD values decreased as the injection pressure increased.

Biodiesel is one of renewable and environmentally friendly biofuels that can be used in the diesel engine with little or no modification in the engine. In the present paper، the performance and emission characteristics of conventional diesel fuel and biodiesel blends produced from soybean oil (B2، B5 and B10) were compared. Tests were performed at steady-state conditions in a direct injection diesel engine with 90 kW power. During the test، the fuel consumption and pollutant emissions were measured. Experimental results showed that relative to diesel، biodiesel had an approximately 5-8% increase in the brake specific fuel consumption (BSFC) due to the lower heating value (LHV) of biodiesel. However، biodiesel significantly reduced carbon monoxide (CO) and unburned hydrocarbons (HC)، while nitric oxides (NOx) and carbon dioxide (CO2) emissions increased slightly. Observations showed that the smoke decreased significantly، due to the oxygen availability of the biodiesel fuel.

Cylinder deactivation is one of recent technologies that reduce the fuel consumption and exhaust emissions. This technology deactivates some cylinders; when there is no need to their output torque. Increased fuel efficiency، decreased emissions from deactivated cylinders and better breathing capacity are results of deactivation. In this paper، a four-cylinder spark ignition (SI) engine has been chosen as a case study. First، all parts of the engine were modeled in the GT-POWER software and then، the model was validated. The second part of this study includes deactivating of cylinders. Results showed advantages in the fuel efficiency and exhaust emissions.

Impacts of traffic conditions on exhaust emissions and the fuel consumption of passenger cars in Arak city have been investigated in this paper. For this purpose, several measurements in various routes of Arak city at different time intervals using GPS system were investigated. 212245 raw samples have been gathered and classified as 2340 separate micro trips. The micro trips were then clustered as three separate clusters using the fuzzy clustering approach. Centers of fuzzy clusters were then selected as the representative traffic conditions, i.e. congested, urban, and extra-urban. Finally, based on representative traffic conditions, the driving cycle for Arak city was developed. Exhaust emissions as well as the fuel consumption of three common vehicles in Arak city including Samand with national engine with gasoline fuel, Samand with the national engine with CNG fuel, and Pride were estimated at various traffic conditions using a backward-facing simulation approach. Simulation results revealed that conventional ECE-EUDC and TEH-CAR driving cycles could not give a good estimation of the fuel consumption and exhaust emissions in Arak city. Moreover, traffic conditions had a considerable impact on exhaust emissions and the fuel consumption in Arak city, as a drastic increase in the fuel consumption was reported; while vehicles were experiencing congested traffic conditions. At the same time, despite prior expectations, due to specific nature of the congested traffic condition in Arak city, not only HC and but also CO and NOx emissions were increased.

Exhaust system is one of the most important parts of the engine، in which two major parameters including back pressure and noise are considered in the design. The goal of the present work is to simulate and validate the noise and the exhaust gas flow of a three-liter turbo-charged diesel engine with the maximum power of 98 kW by the FLUENT software. Afterwards، the pipe diameter of the exhaust system was optimized in order to maximize the engine power by the GT-POWER software. As the increase of the engine power caused the rise of the exhaust gas noise، the optimum shape of the exhaust muffler was represented. Results showed that 1% increase in the predicted engine power by optimizing the size of the exhaust pipe system. In addition، the proposed muffler with the elliptical enclosure and un-aligned inlet and outlet pipes had minimum back pressure and outlet noise.