نشریه تحقیقات موتور
پیاپی 38 (بهار 1394)

In this paper a combined fuzzy-PID controller for idle speed control of internal combustion engine has been developed. The main purpose of this controller is appropriate engine operating under normal and transient loads and reduction of emission and fuel consumption. Using the approach of model based controller design, first, an engine model for the idle state has been developed. In this model idle air valve command and ignition angle are used as inputs and engine speed has been calculated as output. In order to evaluate the behavior of the model, XU7-1761cc gasoline engine data has been used within the idle state. Average error for developed model is 2.33% and maximum error is 8%. Speed control is performed by two new Fuzzy and Fuzzy-PID controllers. Ignition angle and idle air valve opening rate are two outputs of the controlled transient conditions under applying external load such as air condition, power steering and alternator have been simulated. Simulation results show that designed controller has stable and acceptable behavior under transient load condition and reduces fuel consumption up to 14.4% compared to the feedback-feedforward controller implemented in electronic control unit of the vehicle.

As a recently introduced method, entrance fuel magnetization, which is obtained from an external magnetic field, is a process through which exhaust gas emissions and fuel supply of internal combustion engines decrease. One of the preconditions of using the magnetized fuel in internal combustion engines is studying about the effects of fuel change on vibration behavior of the engines. Vibration of internal combustion engines can cause failure in engine components and agricultural machinery and vehicle’s drivers upset. In this research, diesel fuel in magnetic fields with different intensities of 1000, 2000, 3000 and 4000 Gauss was studied and Vibration signals of six-cylinder diesel engine (tractor MF-399) at five levels of engine speed and in the longitudinal, vertical and lateral directions were measured and recorded. The results show that the Root Mean Square (RMS) amounts of vibration acceleration were the most in the lateral direction and the least in the longitudinal direction (75.78 m/s2 and 44.59 m/s2 respectively). This research also shows that the RMS amounts of vibration acceleration decrease by increasing the magnetic field intensity and the lowest value of RMS belongs to a magnetic field intensity of 4000 Gauss.

Both of the exhaust and intake valves are very important components of a diesel engine which are used to control the entrance and exhaust of gases in internal combustion engines. During opening and closing, these valves are subjected to high temperature, spring force and high pressure (up to 15 Mpa) inside the cylinder. Various factors, including mechanical fatigue at high temperatures, thermal fatigue, reduction their mechanical properties such as hardness and yield strength due to heating, wear caused by impacts, especially at the seat and the guide sections, corrosion, excessive heating and accumulation of soot on the valve can be caused to failure of the valve. However, the valves are mainly failured by fatigue. The temperature of internal portions of intake valve and exhust valve are 550 °C and 800-900 °C, respectively. Therefore, these parts are subjected to thermal loading and chemical corrosion at high temperatures. In this research, the failure causes of a bus exhaust valve were studied using chemical analysis, macroscopic and microscopic investigations by optical and scanning electron microscopes and hardness test. The results of chemical analysis and hardness was in accordance with the relevant standard, However, results of macroscopic and microscopic investigations Were indicative of formation of microstructural defects due to increased temperature. Therefore,it was found that the probable cause of failur is the improper performance of the engine which results in excessive rising of temperature and finally causes to failure of valve.

In this study, the combustion process and emission formation using a blend of biodiesel and diesel fule in the in-direct-injection diesel engine) Lister 8.1(at full load states have been simulated with a computational fluid dynamics (CFD). The utilized model was included detailed spray atomization, mixture formation and distribution model which are enable to modeling the combustion process in spray/wall and spray/swirl interactions along flow configurations. Simulation of combustion and expansion stroke was done, therefore qualitative analysis was presented. The results revealed that increasing the percentage of biodiesel in the fuel caused to increase indicated power, indicated specific fuel consumption and peak cylinder temperature. Also results showed that UHC and soot emissions decreased but NOx emission was increased. The results of this research in compare with the corresponding results in the literature and showed a good agreement.

In this study, biodiesel fuel was first produced by converting non-edible rapeseed oil through the transesterification reaction. The functional characteristics of a single-cylinder diesel engine running on a fuel mixture of diesel #2 (2-D) and biodiesel (containing 5, 10, 15 and 20 v/v %) was analyzed under 25, 50, 75 and 100% loading at different engine speeds of 1800 to 3000 rpm with 400 rpm increments. Results showed that higher biodiesel to pure diesel ratios first reduced engine power and torque and then improved them, whereas the engine's specific fuel consumption first was increased and then decreased. Compared to the pure diesel fuel, engine power was increased by 0.97, 0.11 and 4.28% while running on B15, B10 and B20 fuel mixtures and decreased by 3.87% while on B5. Additionally, the B5 mixture at 2600 rpm had the largest impact and the B20 mixture at 3000 rpm had the smallest impact on engine power. B5 under 25% loading and B10 under 100% loading had the largest and the smallest impacts on specific fuel consumption, respectively. Finally, B10 at 2600 and under 100% loading was selected as the best mixture.

Reactivity Controlled Compression Ignition engines are today considered as a subdivision of HCCI engines which can control and manage the combustion process and emission production with using two different types of fuels. Combustion process in these types of engines is initiated by varying the amount of different fuels consequently, varying the reactivity of fuel in various speeds and loads. For this reason, the mixing ratio of the fuels is of great importance. Altering the fuel reactivity also affects the production of emissions. In these engines, fuel with lower reactivity is injected into intake manifold and fuel with higher reactivity is injected directly into the combustion chamber. The port injected less reactive fuel is used to achieve higher efficiency and better combustion in higher compression ratios while the fuel with higher reactivity is used to control the chemical reactions rate as well as to decrease the amount of produced nitrogen oxides and soot. In this work, previously developed chemical mechanisms for N-Heptane and Iso-Octane are used to simulate chemical reaction rates. Iso-Octane has been used to represent the fuel with lower reactivity while N-Heptane has been used as the fuel with higher reactivity. In the first step, the effects of Iso-Octane and N-Heptane existence are discussed and then important combustion parameters such as emission, knock and incomplete combustion are investigated in case of changing the both fuels ratios.