نشریه تحقیقات موتور
پیاپی 22 (بهار 1390)

In this study, an in-house multi-dimensional code has been developed which simulates the combustion of n-heptane in a Homogeneous Charge Compression Ignition (HCCI) engine. It couples the flow field computations with detailed chemical kinetic scheme which involves the multi-reactions equations. A chemical kinetic scheme solver has been developed and coupled for solving the chemical reactions and calculation of heat release. The effect of parameters such as, initial temperature, initial pressure, compression ratio and equivalence ratio on the combustion characteristics of a n-heptane fuelled HCCI engine have been studied. The chemical kinetic scheme used here, consists of 27 elementary reactions and 26 species which involves the reactions required for calculation of NOX also. The results show good agreement with available experimental data.

Great effect of three way catalytic convertor (TWC) performance on oxygen sensor output voltage has made the sensor (located after catalyst) as the main signal in almost all today’s TWC monitoring algorithms. In this paper output voltage of nonlinear oxygen sensor is estimated using a nonlinear autoregressive with exogenous inputs (NARX) model. The estimation uses ECU calculated exhaust gas flow and air fuel ratio from upstream lambda sensor and does not need any unconventional sensor measurement. Combined with simple structure applied to the NARX model, an algorithm applicable to real-time computations on vehicle is designed. Estimated voltage is compared to real measurement from a car during new European driving cycle (NEDC), showing good performance of the estimation algorithm. Moreover, by tests results it is shown that this model can monitor the effect of catalysts aging.

The premature breakage in some four cylinder diesel engine crankshafts was reported. All crankshafts were failed from the same region. Failures had been occurred in the first crankpin, the nearest crankpin to the flywheel. Dynamic analysis and finite element modelling were carried out to determine the state of stress in the crankshaft. FEM results revealed that the first crankpin fillet is the most vulnerable point to fracture. Soderburg diagram of the studied crankshaft showed that the service operation point, which stands for mean and alternating stresses of the critical region (first crankpin fillet) was located in the safe region. Therefore, it can be concluded that fatigue fracture has not occurred in the crankshaft. SEM images of the fractured surface also showed cleavage fracture and put in evidence that the failure was brittle fracture. No sign of fatigue failure was observed. The fracture may be caused by an overload. However, the results suggest re-evaluation of the design and manufacturing. The fillet rolling may play an important role in this matter. Optimization of the fillet rolling process by changing process parameters has been recommended to the manufacturer. This recommendation has been adopted by the manufacturer and no further fracture has been reported since.

The purpose of this study is to investigate the effect of injection parameters on a heavy duty diesel engine performance and emission characteristics. In order to analyze the injection and spray characteristics of diesel fuel with employing high-pressure common-rail injection system, the injection characteristics such as injection delay, injection duration, injection rate, number of nozzle holes were investigated by using a quasi- dimensional model. In this work, different injection rate is considered with various injection parameters and performance and emission of the engine is simulated.The aim of this work is finding the best injection system for a high efficiency and low NOx emission heavy duty diesel engine.

This research uses computational modeling to explore another method to increase diesel engine performance while maintaining low pollutant emission levels. Previous studies have shown that injection-rate profiles and injector configurations play important roles on the performance and emissions of particulate and NOx in DI diesel engines. Since the most important engine design parameters, including filling efficiency, flame stability, performance and pollutant formation depend on the local flow field in inlet port and then in cylinder, the ability to accurately predict these more details is a key requirement for successful application of computational fluid dynamics techniques to design and optimization engines. In this work which is done at Motorsazan.Co in order to optimize inlet port shape, a procedure is outlined for producing a computational mesh for intake port and in-cylinder geometry on 135TI diesel engine at various intake port shapes. After modeling the combustion chamber with inlet port, AVL FIRE software has been employed for grid generation and numerical simulation in an open cycle mode. The numerical results are validated by corresponding experimental data for base line engine. Concerning the design limitations, two new helical ports are introduced and simulated using the same solver, boundary and initial conditions. Final performance and pollutant emission results, obtained from new models are compared with those of the base model and the model with the best results is introduced as the optimum among all. This work demonstrates that multidimensional modeling at an open cycle can now be used to gain insight into the combustion process and provide direction to explore new engine concepts.

Basic understanding of the process of coolant heat transfer inside an engine is an indispensable prerequisite to devise an infallible cooling strategy. Coolant flow and its heat transfer affect the cooling efficiency, thermal load of heated components, and thermal efficiency of a diesel engine. An efficient approach to study cooling system for diesel engine is a 3D computational fluid dynamics (CFD) calculation for coolant jacket. Therefore, computer simulation can analyze and consequently optimize cooling system performance, including complex cooling jacket. In this paper a computational model for boiling heat transfer based on two-phase Mixture model flow is established. Furthermore, the phenomenon of nucleate boiling, its mathematical modeling, and its effect on heat transfer is discussed. Besides, the static, total pressure, velocity and stream lines of the flow field, heat flux, heat transfer coefficient and volume fraction of vapor distribution in the coolant jacket of a four-cylinder diesel engine is computed. Also, comparison between experimental equation (Pflaum/Mollenhauer) and two-phase Mixture model for boiling hat transfer coefficient is done and good agreement is seen. In conclusion, it is observed that at high operating temperatures, nucleate boiling occurs in regions around the exhaust port. Numeri­cal simulation of boiling heat transfer process of cool­ing water jacket and temperature field in the cylinder head of the diesel engine is compared with the data measured on the engine test bench. The calculated results indicate that this method can reflect the impact of boiling heat transfer on water jacket rather accurate. Therefore, this method is benefit to improve the computational preci­sion in the temperature field computation of a cylinder head

In this study is designed a heat exchanger for cooling exhaust gas and is carried out an experiment to investigate the effect of Exhaust Gas Recirculation (EGR) temperature on destruction of the fuel’s availability due to combustion processes in IDI diesel engine cylinder. To serve this aim an exergy analysis is conducted on the engine cylinder which provides all the availability terms by which the evaluation of in-cylinder irreversibilities is possible. The availability terms including heat transfer, inlet and exhaust gases and work output are presented during the engine operation at different load and speeds. To clarify the effect of using EGR in each case, EGR is introduced to the cylinder at various ratios and temperature during the tests. The results show about 60 to 70 % of fuel’s availability destroyed by irreversibilites. Also the results reveal that the increase of EGR temperature leads to reduce of combustion irreversibility. But On the other hand the increase of EGR temperature lead to heat and availability are dissipated of the wall and exhaust gas. So depend on the engine operation at different load and speeds, the increase of EGR temperature could be lead to a positive or negative effect on the engine performance