نشریه تحقیقات موتور
پیاپی 25 (زمستان 1390)

In this paper، critical speeds of an engine were found with different conditions of engine working and the alternator. Critical speeds occur whenever the belt has maximum oscillations. During a test at critical speeds، several variables were measured. The variables were the belt length، the mass and the stiffness. Belt performance variables such as the cooler compressor pressure and temperature of the alternator were measured، too. To measure the amount of the belt slippage، the difference between ideal and actual pulley rotational speeds was calculated. Results showed that the pressure of the cooler compressor increased by increasing the belt length but the temperature of the alternator was not changed. Also، parameters of the belt such as its length، oscillation، temperature and hardness affected each other.

Nowadays، the homogenous charge compression ignition (HCCI) engine is a new idea to satisfy two main strategies in the design of internal combustion engines: reducing the fuel consumption and emissions. The robust control of combustion phasing in HCCI engines is a main challenge limiting the automotive industry for the mass production. In controlling combustion phasing and the IMEP (as two main controlling parameters) in the HCCI engine، some parameters are more effective than others. Effects of these parameters such as the inlet temperature and pressure، the equivalence ratio، the engine speed and also PRFs on the start of the ignition and the IMEP have been investigated in this study using a thermo-kinetic zero-dimensional model. This model coupled to a full kinetic mechanism of PRFs. The model was validated with a large number of experimental data taken from the Ricardo engine. Results show that the start of the combustion depends on the inlet temperature، the octane number، the engine speed and the equivalent ratio. On the other hand، the IMEP depends on the fuel mass flow rate، the inlet temperature and the equivalent ratio. As a result، a correlation has been presented to predict the start of the combustion and the IMEP; and its accuracy has been checked with some experimental data.

A theoretical model is presented in this research to predict the ignition delay and the combustion process in a class of stratified charge engines including the non-spherical flame progress through rich and lean regions. Step by step calculations were carried out in both rich and lean regions. The process continued until all the fuel was burned. At each crank angle، the volume of the mass control changes and the mole fraction of the burned fuel increased due to the flame propagation. Considering the heat transfer from the cylinder contents to the surrounding area and the frictional work، some important operating parameters such as the mean effective pressure، the thermal efficiency and the specific fuel consumption، were predicted. Predicted values obtained by the model for the natural gas were compared to corresponding experimental data. The comparison shows that there is a logical agreement between theoretical and measured values. The flexibility of the model allows having accurate predictions in a wide range of the charge stratification for various hydrocarbon fuels.

The prediction of the droplets diameter and the velocity distribution in a spray is very difficult، since its processes and mechanisms are not completely known and depends on many parameters. The early stage of the atomization process (Primary Breakup) is clearly deterministic، whereas the final stage of the spray formation (Secondary Breakup) is random and stochastic and deals with the stochastic aspect of the droplet size and the velocity distribution which is done using the maximum entropy principle (MEP). The MEP predicts the atomization process while satisfying constrain equations of the mass، the momentum and the energy. Finally، experimental results for an annular jet and a swirl nozzle were used to verify the modeling results for the size and the velocity distribution of spray droplets which shows a good agreement between modeling and experiments. The effect of some atomization parameters like Weber number، momentum and energy source terms were investigated on the droplets distribution.

In this paper، the life expectancy of the engine oil in 70 diesel engines installed in super heavy vehicles (the E6-350 ECONODYNE 4VH model) has been estimated using oil analysis. The method which used، was to change the used oil based on oil operating hours، odometer and taking samples. Then، the oil sample was sent to a laboratory for the analysis. In order to be able to determine the overall condition of the engine، we had to study various parameters، such as the viscosity، the base number، the acid number، the type and the amount of the engine wear in the same condition of the engine model، the oil consumption and the operating conditions. Therefore، the oil life expectancy would be determined. If the number of samples increases، then the value of errors will be reduced. Results would merely be based on the number of samples.

One of the major goals for manufacturers of turbocharged spark ignited (SI) engines is to increase the knock resistance at high loads. In order to move out of knocking combustion، timing of the spark ignition is retarded، thus limiting the maximum pressure and temperature in the combustion chamber. This is an effective method to eliminate the knock. The negative effect of retarding spark timing is increasing the exhaust gas temperature. In order to reduce the exhaust gas temperature، rich mixtures are normally used. As a result، the fuel consumption increases. The cooled EGR can be used to solve this problem. Using the cooled EGR decreases the pressure and the temperature in the unburned zone. There are a number of different possible architectures، each with its specific characteristics. Main objectives of this study were to quantify the increase the knock resistance and to decrease the enrichment in order to the target stoichiometric operation over the full operating range. All the simulations were carried out in the GT-POWER Software on the EF7-TC engine.