جستجوی مقالات مرتبط با کلیدواژه « پیش محفظه احتراق » در نشریات گروه « مکانیک »

In this paper, the thermodynamic modeling and analysis of various components of a turboprop engine and their relation in the steady-state design and off-design performances are addressed. An algorithm is presented and a computer code is developed for the analysis of the cycle in design and off-design conditions. Then off-design performance curves are plotted for different turbine inlet temperatures, flight elevations and Mach numbers and their results are interpreted. The results are compared and validated with the results of GasTurb software. In addition, the effects of the combustion chamber defects on the performance of the engine are investigated. The results of this paper can be used as the first step in the study of the performance and upgrading of these engines. The results of this study show that the specific fuel consumption will rise by 14% for a 10% increase in the combustion chamber pressure drop. Furthermore, the specific fuel consumption increases by 13% and the engine power reduces by 17.5% for a 10% reduction in the combustion efficiency.

Following concerns about air pollution and global warming in recent years, the use of heavy duty gas engines has become favorable in major industries such as the marine industry, power plants, etc. Heavy duty diesel engines designed for similar applications were used and made by modifying their structure or adding new parts or a combination of the two approaches, because of the fact that heavy duty gas engines are more similar to diesel engines with similar emissions. They have less emission and also less power. Various technologies can be used to increase the power of the gas engines. One of these new technologies is the pre-combustion chamber, which results in an increase in power output. The pre-chambers are categorized into two types of refueling in terms of how the refueling is shared with the main chamber and refueling independent of the main chamber. The pre-combustion chamber should be used to increase the efficiency of the pre-chamber and overall engine efficiency, which is suggested after considering the use of the pre-combustion chamber with a stand-alone fuel system.

Controlling the gas turbine emissions has led the manufacturers to use new technologies. Nitrogen oxides (NOx) are one of the major pollutants of gas turbines with natural gas as fuel. Thermal NOx is the main cause of NOx formation in gas turbines at high temperatures. So, water injection can be useful in reducing the NOx emission. In addition to NOx reduction, water injection causes an increase in carbon monoxide emission and damage to combustion chamber. Therefore, it is desirable to find the optimum amount of water injected to the combustion chamber to meet the regulations. To find the optimal water mass flow rate, we numerically investigated the combustion inside the chamber for full load and part load before and after water injection. Then, the effect of water injection at different flow rates was studied to obtain optimal water flow rate. The results showed that for the full load, the optimal water flow rate was 100% of the fuel flow rate and the upstream pressure of the feed water system was 24.45 bar. For the part load (fuel flow rate equals to 75% of the full load), the optimum water injection rate is 80% of the fuel flow rate. In this case, the pressure required for water injection is about 16.5 bar. Results also show that the change in water temperature in the range of 10-80˚C has no significant effect on NOx formation and water can be injected at the ambient temperature.

Using GDI technology has a lot of challenges for automotive manufacturers such as a combustion development so PFI engines have been produced and even, in some markets, their production is increasing. Regarding to the strict emission legislations, PFI engines need improvement and using novel technologies. One of these technologies is APFI concept. This concept could approximately achieve the main advantages of GDI technology by less cost and challenges. In this study, the effect of APFI on the wall wetting, fuel distribution in combustion chamber and output power are investigated. It shows that using this concept could decrease fuel film mass on intake system about 75 percent. In the other hand, fuel distribution in combustion chamber (around spark plug) becomes homogenous which causes improvement in combustion progress and increases in-cylinder peak pressure. Investigations show that the APFI engines are sensitive to the injection timing so the optimum time for start of injection is investigated.

In this paper, a hybrid motor performance with high density poly ethylene (HDPE) as fuel and gaseous oxygen (GOX) as oxidizer was studied. Oxidizer was injected into nozzle with an axial injector. Effect of parameters such as mass flux, combustion chamber pressure, and distance from grain lead were studied through tests and by means of data reduction techniques. Besides, effect of utilizing pre-combustion chamber was studied. It was shown that using pre-combustion chamber helps to have an even regression in axial direction. In this case, regression rate was independent from axial location from grain lead. Dependency of regression rate to combustion chamber pressure was also determined which showed a good agreement with available empirical data. Finally, a classic regression rate relation for poly ethylene was determined in terms of total mass flux and combustion chamber pressure.

In this study, a numerical model has been developed in AVL FIRE software to investigate combustion and injection inside the cylinder of a direct injection spark ignition CNG engine. In this regard two parts have been taken into consideration. In the first part of the study, gas injection via a single-hole injector into the cylinder with five different piston head geometries has been investigated. Using quantitative and qualitative representations of the results, the suitable combustion chamber geometry for DI application has been discussed. In the second part, combustion studies have been performed based on the selected geometry from the first part. Spark plug location and ignition timing have been investigated as two of the most important combustion variables. Five different configurations for the spark plug have been taken into consideration and the idea of using two spark plugs has been also tested, where it showed the best combustion characteristics. The spark timing has also been studied based on the selected configuration. The results show that ignition timing should be at 50 degrees before top dead center in order to have the best combustion characteristics.

One of effective and important parameters on gas turbine output power is the ambient air temperature and increase of 1 degree centigrade of this parameter decreases output power of total cycle about 0. 6 to 0. 9 percent. Compressor inlet cooling is a useful way to increase of turbine power output. In this paper different ways of compressor inlet cooling such as evaporative cooling and refregerative cooling method are reviewed and at the end، direct jetting method (fogging method) is focused. Additionally thermodynamic modeling of cycle elements are studied and water jetting effects on operating parameters of GE - F5 gas turbine of Mashhad Power plant with consideration of cooling effect and humidity in combustion chamber and combustion modeling with humidity effect are presented. This study shows that 22 ℃ compressor inlet air cooling prevents power losing of total power plant cycle about 18. 79 percent in optimum case of operating.

Internal combustion engines are used as stationary engines in factories and power plants for a long time. In recent years, the demand for environmental protection and the use of alternative fuels have excited the product market to the power generation systems using heavy duty gas engines. This research activity investigates the effect of piston bowl depth on the performance and emissions of gas engines. Towards this purpose, 3D computational fluid dynamic is used to simulate the cycle engine. By implementing the equations of combustion, turbulence and pollution, close cycle of engine is simulated and the results are presented as graphs and contours. Firstly, results are validated with experimental data and the by simulating of three different pistons, their pressure and temperature inside the cylinder and their amount of emissions are compared.The results show that combustion chamber which creates best mixing and optimum turbulence has the best performance and releases lower emissions.