Abstract
Natural gas is used as alternative fuel in speak ignition engines in many countries to satisfy air quality standards. Gas engines can be operated in stoichiometric and lean burn condition with different combustion and emission details. In this study a natural gas spark-ignition engine at stoichiometric condition was optimized to avoid knock occurrence. Compression ratio and engine speed were optimized to obtain the lowest fuel consumption accompanied with high power and low emission. A quasi-dimensional two-zone combustion model was developed to simulate combustion and a knocking model was incorporated with main model to predict any auto-ignition that might occur. The model was validated by comparing with available experimental results. Performance parameters and exhaust emissions were also computed by using this model. It was found that using cooled EGR especially at high compression ratios has a key role in reducing NO emission.
Highlights
Natural gas has been used as alternative fuel in speak ignition engines form the early 1980s [1]
The main motivations in using natural gas are: 1.NG engines are able to operate at high compression ratios without knock occurrence; 2.Engines running on natural gas emit significantly lower emissions compared to engines running on conventional fuels
Intake mixture condition to avoid knock occurrence and obtain low emission and high performance In order to simulate turbocharging behavior, all investigations were made at inlet pressure of 210 KPa
Summary
Natural gas has been used as alternative fuel in speak ignition engines form the early 1980s [1]. Another method to control NOx emissions is to retard the spark timing, which leads to a decrease in engine efficiency and an increase in HC emissions It would be difficult for the conventional gas engine operating on lean burn mode to meet the stringent future emission standards especially for NOx emissions [6]. The alternative technique that has been used for four decades is the use of a three way catalyst (TWC) to reduce NOx, HC, and CO emissions [7] It is much less expensive than the SCR devices used in lean burn engines. When the engine operates near the stoichiometric mixture, the in-cylinder temperature increases, and the thermal stresses and the knocking tendency increase This would lead to some restrictions on the use of turbocharging, high compression ratio, and maximum brake torque (MBT) spark advance timing. In this study a quasi-dimensional two-zone combustion model was incorporated to simulate the in-cylinder conditions of NG engine
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