THE JOURNAL OF ENGINE RESEARCH
Year:2008 | Volume:5 | Issue:12|Papers Count:7

In the present research a single-zone theoretical model based on the first law of thermodynamics has been employed to predict the performance of a HCCI engine using ethanol fuel. Combustion modeling is based on chemical kinetics of the fuel using CHEMKIN library. Equations related to fuel reaction rates. thermodynamic and transport properties as well as heat transfer from in-cylinder contents to surrounding surfaces are simultaneously solved. Effects of fuel air equivalence ratio on combustion has been evaluated and predictions for in-cylinder pressure and temperature as well as mole fractions of cylinder contents are compared with the corresponding theoretical and experimental values reported in the literature, to assess accuracy of the presented model. The results show reasonable compatibility.

Blowby and gas flow through the cylinder-pis ton-ring crevices are phenomena affecting the engine performance and the amount of exhaust pollutants. Also these phenomena affect the cylinder pressure, cyinder temperature and the charge amount during a cycle. The study and validation of a sub-model for these phenomena in the absence of combustion deducts the effects arisen from the combustion event. In the present study, blowby sub-model and gas flow through crevices under motoring conditions have been investigated using a volume and orifice theory and the experimental results are measured from a research engine. Blowby geometric parameters, consisting of a few critical cross-sectional areas (orifice areas) and volumes (top land and inter-ring crevice volumes), were measured in ambient temperature and corrected for hot running conditions. The cylinder pressure during the cycle operation was measured by a piezoelectric pressure transducer and the low pressure parts of the cycle were measured using a piezoresistive pressure transducer for referencing purposes. The obtained results showed a very good agreement between experimentally measured pressure data and model output for three compression ratios of 7.6, 10.2, 12.4 and three engine speeds of 750, 1500 and 2000 rpm, so that the maximum deviation was almost 5%. The model prediction shows that the maximum mass loss increases by increasing the compression ratio and decreases by increasing engine speed. Also the peak mass loss position occurs within the range of 3 to 9°CA after Top Dead Center. Since then, a reverse flow from the top land crevice into the cylinder is predicted in the model.

LM13 alloy is widely used in piston industry due to its low coefficient of thermal expansion, excellent castability and hot tear resistance. In this research, effect of casting process on wear behavior of LM 13 alloy was investigated. First, samples were produced using two casting processes and heat treatment. Then wear behavior of these samples under dry sliding condition was examined. Results of hardness and strength tests indicated that squeeze cast specimens exhibited higher mechanical properties. Wear experimental results showed that in both squeeze and gravity cast specimens, the amount of weight loss increases with increase in sliding distance which is accompanied by reduction in wear rate and friction coefficient. A comparison between two samples demonstrated that squeeze sample had better tribological behavior. Casting process variation causes decrease in friction coefficient from 0.4 to 0.2 for squeeze cast samples and decrease in weight loss of these samples. Squeeze cast samples had better surface quality and in these samples abrasive, adhesive and delamination are dominant wear mechanisms, while in gravity cast samples abrasive, adhesive and surface fatigue are the dominant wear mechanisms.

Appropriate turbocharger selection in matching the turbocharger to an internal combustion engine is a complex process, in which several parameters should be accounted. Turbocharger matching should be performed in a way that high efficiency in the wide range of engine operation to be obtained. In the turbocharger matching, not only compressor but also turbine should perform acceptable performance in the range of engine operation. In matching procedure, first, the performance maps of turbine and compressor should be determined experimentally or theoretically. In this paper, performance characteristics of twin entry radial turbines are determined. This procedure is based on steady state one-dimensional modeling of turbine using governing equations considering loss coefficients. In the turbocharger Lab., the performance characteristics of the turbines have been determined experimentally in the wide range of operation conditions. Comparing modeling results with the experimental data shows good agreement. Finally, the CNG engine performance is simulated and compared with the experimental results. These two simulations are employed to match the turbine to the engine. The results of matching two turbines with different geometry to the engine show that one of the turbines presents appropriate matching to the engine in the range of engine operation with the highest efficiency.

A thermodynamic model has been developed in this paper for an SI engine fueled with methane. The model is two-zone (burned-unburned) considering the chemical kinetics of methane burning. The reduced burning mechanism includes 20 reactions with 15 chemical species. It was assumed that the flame, with adiabatic temperature is in equilibrium stage. The unburned zone was considered extensively to analyze the conditions that lead to knock. The 'Knock Criterion' has been used to forecast the knock intensity. The influence of engine parameters such as spark advance, compression ratio and relative humidity of air intake has been studied on knock phenomenon. The experimental engine results from the literature were used to validate the accuracy of our model. The results show that any increase in spark advance and compression ratio or decrease in humidity of air intake wills increase-the probability of knock in the engine.

Using CNG as an alternative fuel is in matter of consideration for a few recent decades. Because of its superior combustion characteristics and low emissions, it could be a remarkable preference for the upcoming generations. In this research, the model of naturally aspirated M355G diesel engine has been developed and using this model, a desirable matching of engine and turbocharger has been achieved and the required characteristic curves have been resulted. Furthermore, an experimental investigation was conducted on both naturally aspirated and turbocharged engine, and consequently an appropriate evaluation of model was maintained.

The main goal of this research is to compare the fuel spray penetration of a naturally aspirated engine with the same turbocharged diesel engine in road load conditions, both experimentally and theoretically. In the experimental part, a lorry with a naturally aspirated OM314 diesel engine has been utilized in road test under the different operational conditions for determining the road load power. Then in the diesel laboratory, a naturally aspirated OM314 diesel engine and a LIMP turbocharged OM314 diesel engine has been tested under the road load conditions to measure the required parameters. In the theoretical part, we have developed a new parameter based on the Dent correlation and the ideal diesel cycle, which is called fuel spray penetration (FSP) ratio. This parameter calculates the fuel spray penetration in a turbocharged diesel engine in comparison with the same naturally aspirated diesel engine. By means of the experimental data, FSP ratio has been calculated for different operational conditions. Results show that while the gauge inlet manifold pressure is 0.2 bar, the injection pressure should be increased by 50 bar to compensate for the increased cylinder pressure due to turbo-charging. Also the optimum fuel injection pressure has been investigated by the ECE-R49 standard test. Experimental results show that when the injection pressure reaches to 250 bar, soot emission reduces around %16.