نشریه تحقیقات موتور
پیاپی 40 (پاییز 1394)

Internal combustion engine is one of the vibration sources in an automotive. In this study, proper stiffnesses for engine mounts of national engine are determined to improve its vibration behavior. At first, complete mode decoupling about torque roll axis is considered. However, the results show that complete decoupling is impossible. Therefore, partial mode decoupling is performed about torque roll axis. In this regard, an optimization problem is solved to achieve maximum percentage of mode decoupling about the mentioned axis. Finally, frequency response diagrams for displacement and rotation of engine, as well as, for transmitted force to the chassis are presented for nominal and optimized stiffnesses. The obtained results show that the engine movements and transmitted force to the chassis are reduced and therefore vibration behavior of the engine mounting system is improved by employing the mentioned partial mode decoupling.

As motorcycles are named as one of the important air pollution emission sources in Tehran, investigating their emission performance and finding a solution for reducing their emission is of high importance. In this study, emission factors from 60 motorcycles from Tehran’s present fleet and 4 closed loop injection fuel supply system and catalytic converter equipped motorcycles were measured. Measurements were taken in chassis dynamometer Laboratory according to Euro-3 standard procedure in ECE driving cycle. Tests results showed that CO emission factor from Tehran’s present motorcycles are 7 times higher than Euro-3 certification limit. It was indicated that about 40% of carbon in fuel burns to incomplete combustion product in Tehran’s present motorcycles. Using carburetor fuel supply system is responsible for this emission performance. Test results showed that CO and THC emission factors of injection and catalyst equipped motorcycles are 87% and 75% less than that of Tehran’s present motorcycles respectively. Total pollutants emissions caused by Tehran’s motorcycles in morning peak hour were estimated. It was revealed that, by replacing Tehran’s present motorcycle with closed loop injection fuel supply system and catalyst equipped motorcycles, CO, THC and NOX emissions from motorcycles in morning peak hour would reduce by 88, 88 and 46% respectively.

Main purpose of this paper is investigating on the effect of reformer gas on the HCCI combustion of blended fuels. A validated multi zone model coupled with a semi detailed chemical kinetics mechanism. Chemical kinetics mechanism contains 101 species and 594 reactions. Reformer gas is considered as a mixture of carbon monoxide and hydrogen and five different values of it are added to base fuel. Base fuel in this study is a mixture of n-heptane and iso-octane and three different compositions containing PRF20, PRF40 and PRF80 are focused. Results show that reformer gas addition retards the start of combustion, and reduces in-cylinder peak pressure and temperature. Reformer gas addition affects combustion duration and exhaust emissions. Exhaust carbon monoxide and unburned hydrocarbons increase and nitrogen oxides decreases by increase of reformer gas concentration.

In this study, performance of oil droplet separator in crankcase ventilation system for three engines, Ford-Ecoboost (impactor with variable area), Nissan-vq37de (inertial impactor), and Peugeot-Xu7 (cyclone) at the same volumetric flow rate has been studied experimentally. Because of the complexities of geometrical and functional in internal combustion engines, a test rig is designed to study the separation of engine oil droplets with a diameter of 0.1 to 10 µm of gas leakage (blow-by), in this experiment, a special oil atomizer implemented for the production of micro droplets, similar to the drops in engine blow-by. Tests were done in two volumetric flow rate 16 and 24 L/min. To ensure the accuracy of the results of designed test rig, all the tests were repeated at least three times for each volumetric flow rate. Gravimetric method was implemented to estimate the separation efficiency. According to the results of the tests it was found that the separation efficiency of impactor with variable area is better than similar models, so that at the same flow rate of two phase air-oil flow, efficiency of impactor with variable area is almost eight times that of similar models. In this article, pressure drops of flow of the mentioned separators were also measured experimentally. Although the efficiency of impactor with variable area is more than the other impactors but its pressure drop is lower than Nissan’s impactor.

In recent years several studies have been done in the field of laminar flame speed. One of the important characteristics of the combustion is the laminar flame speed. In this study, the effects of CO2 and N2 on the laminar flame speed of natural gas and gasoline fuel mixture have been investigated. Schlieren method has been used in this study. Experiments were carried out at pressure of 1 bar and 363 k in constant volume chamber. The mass fraction of CO2 and N2 varied from 0% to 12%.The result shows laminar burning velocity and the adiabatic flame temperature decrease with the adding CO2 and N2 Specific heat capacity of CO2 more than N2, for this reason the laminar burning velocity of N2 more than CO2. Also the result shows Addition of CO2 and N2 does not cause much change in stability.

Reactivity controlled compression ignition (RCCI) is a novel combustion concept which uses port fuel injection (PFI) of a low reactivity fuel and direct injection (DI) of a high reactivity fuel with optimum multiple injection to provide a stratified mixture inside the combustion chamber. Piston bowl design has a considerable effect on engine’s pollutant emissions specially unburned hydrocarbons (UHC). This paper studies the influence of piston bowl design on combustion and emission characteristics of natural gas/diesel RCCI engine using CONVERGE CFD. Firstly, the obtained results are validated with the available ones in the literature. Then, three piston bowl designs including stock, bathtub and cylindrical are selected for comparison. The parametric study is conducted at three different engine speeds (i.e., 800, 1300 and 1800 rpm). Effects of piston bowl geometry showed that the optimum piston bowl design from performance and emissions point is the bathtub design.