نشریه تحقیقات موتور
پیاپی 20 (پاییز 1389)

The objective of this work was to develop a new design of an intake manifold through a 1D simulation.It is quite familiar that a duly designed intake manifold is essential for the optimal performance of an internal combustion engine. Air flow inside the intake manifold is one of the important factors, which governs the engine performance and emissions. Hence the flow phenomenon inside the intake manifold should be fully optimized to produce more engine power with better combustion and further reduces the emission.In this paper, during the new engine development the pressure waves for the intake manifold is simulated using 1D GT-POWER software, to study the internal air flow characteristic for the 4-cylinder gasoline engine during transient conditions. Based on the 1D simulation results, the intake manifold design is optimized. As a result of this analysis, intake manifold with 2.5% improvement in volumetric efficiency is achieved.

Current approaches to internal combustion engine analysis are no longer just from first law of thermodynamic's point of view. Evaluation of IC engines by second law of thermodynamics (concept of exergy) helps modifying different parts of engine that cause availability dissipation. EGR method is widely used as an effective method for decreasing NOx as a toxic pollutant in diesel engines. This teqnique decreases the in-cylinder peak temperature by lowering the oxygen concentration. In this experimental investigation is carried out in order to analyze different aspects of using EGR on in-cylinder irreversibility and second-law efficiency within the engine block. It was observed that use of EGR can generally decrease the second-law efficiency in various engine loads and speeds.

In order to reduce wear in gudgeon pin, bush and piston boss lubrication is done. Oil used in national engine species was 10W40 with dynamic viscosity 5.5 mPa.s at 140 °C (the working temperature). In order to complete investigation the oil film hydrodynamics analysis in small end of connecting rod, a real full model engine with four cylinders has been simulated by AVL EXCITE5.1 software. In this software, effect of 6 variables consist of; oil temperature, kind of intake, kind of fuel, tolerance bearings between gudgeon pin and bronze bush, position of bearing and engine speed on maximum pressure and minimum thickness of film were investigated, and each curves of them has been extracted. The effect of six inputs (oil temperature, intake type, fuel type, tolerance, bearing position, and engine rotation speed) on the lubrication parameters was simulated for four different modes of national engine EF7 by neural networks.The results of AVL EXCITE simulation show that Maximum hydrodynamics pressure of oil film occurs at 3500 rpm in 372° crank angle (combustion moment) in turbocharged engine EF7 with CNG fuel was 446 MPa and 1.83 µm respectively at 140°C working temperature of oil. At same condition, minimum hydrodynamics of oil thickness was 1.83 µm, which bearing wear was the possibility. The best neural network FFBP topology for the prediction lubrication parameters (maximum pressure and minimum thickness) was 6-24-30-2 structure with learning algorithm trainlm and functions threshold logsig, tansig and is pureline. This network at 120 epochs, 85.6 second with learning error 0.00229 was convergent. Network error (MSE) for this topology for training, evaluation and testing patterns were 0.0013, 0.0027 and 0.0018 respectively. Also determination coefficient (R2) for this topology for training, evaluation and testing patterns were 0.9952, 0.9988 and 0.9965 respectively.

Today there are different vibration isolators used in industries according to the weight and excitation frequency of the machines which have vibration. One of them is Air Spring which is in two types: Convoluted air spring and membrane air spring. Convoluted air springs are used to control vibrations in low frequency (usually lower than 10 Hz) and the membrane ones are used in high frequency (upper than 20 Hz). Middle frequency is between 10 and 20 Hz. Other vibration isolators are being used for this frequency range. In this paper an air spring system was made using LVDT, as the linear measurement sensor, accelerometer with PID controller and convoluted air spring. As mentioned convoluted air springs are used in low frequency but by using conclusions of this research we can use it in high frequency (about 50 Hz). Finally, an optimum vibration isolator has been made which reduce the vibration amplitude from 2.7 mm to 0.15 mm (about %87.5 reduction in vibration amplitude). Finite element analysis results have been compared with experimental results. There is a good adaption with approximately %8 error. This research has been done according to IPCO request for controlling of engine test stand vibration.

In this paper, the heat balance of an engine was investigated experimentally. The experimental work was conducted on the EF7 natural gas fueled and turbocharged engine. The main goal was to develop an empirical equation to be able to predict the heat balance of the engine at various loads and conditions. The data were collected at four different conditions, two different loads and two different inlet coolant temperatures, to include the effects of these parameters into the empirical equation. The exhaust energy, power, coolant energy, and the other energies were determined either directly from the collected data or indirectly calculated from the data. Based on the experimental results along with the engine specifications, a mathematical equation was suggested. Different types of energy can be calculated from this equation which shows a very good agreement with the experimental data.

Designing and optimization of the intake manifold is one of the important steps in the development of the internal combustion engines. In this paper, the flow inside the intake manifold of an internal combustion engine is investigated by numerical methods. The convective flux models are adopted to simulate the unsteady compressible flow behavior. To solve the governing equations, for calculating the flow specifications, a FORTRAN 90 code was written by the authors by different finite-volume methods. Three schemes, namely second-order averaging, first-order upwind and second-order Roe have been applied and their performance was compared in terms of computational efficiency. The inlet and outlet conditions are modeled by a combination of characteristics and extrapolation. A virtual time method was utilized for simulating the unsteady pulsative behavior. To obtain better accuracy and a realistic flow model, wall friction and heat transfer terms have been included and the effects of friction and heat transfer on flow specifications have been investigated.

Homogenous charge compression ignition engine is a promising idea for reducing fuel consumption and engine emissions. As homogenous mixture of air and fuel is compressed until auto-ignition occurs in HCCI engines, therefore start of combustion is strongly related to chemical kinetic mechanism of fuel oxidation. In this paper, a thermodynamic single-zone model including detailed chemical kinetics is developed to simulate an HCCI engine fueled with methane. The model is validated with experimental results and it is used to study the effects of various parameters such as inlet mixture temperature/pressure and engine speed on the engine performance and start of combustion. Start of combustion is specified via third derivation of pressure trend due to crank angle. Indicated power/ work and specific fuel consumption is utilized to evaluate engine performance.