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Gas Power Cycles
Published in Kavati Venkateswarlu, Engineering Thermodynamics, 2020
Lean-burn combustion is basically burning the fuel with excess air in an IC engine. In lean-burn engines, the air fuel ratio may be as lean as 65:1 (by mass) in contrast to the stoichiometric air/fuel ratio (14.6:1) required to combust gasoline. The excess air in a lean-burn engine leads to complete combustion far less hydrocarbons. High air/fuel ratios will also help in reducing the losses caused by other engine power management systems such as throttling losses. The knock resistance capability of lean mixtures is higher than that of stoichiometric mixtures, permitting the use of high compression ratios. The fuels with high research octane number such as natural gas in a lean burn engine with a high compression ratio can achieve a high thermal efficiency, due to the increased specific heat ratio, lower combustion temperature, and reduced throttling losses.
Introduction to Internal Combustion Engines
Published in K.A. Subramanian, Biofueled Reciprocating Internal Combustion Engines, 2017
Design parameters, such as compression ratio, variable valve timing, and combustion chamber geometry, and operating parameters, such as air-fuel ratio, speed, load, EGR rate, and oxygen enrichment (using membrane system), need to be optimized for reducing PM emission. For example, increasing the compression ratio in an SI engine would lead to high in-cylinder temperature, resulting in better oxidation of particles. The oxygen enrichment using a membrane system will also significantly reduce PM emission in diesel-fueled compression-ignition engines. If the speed of the CI engine increases, cycle time and mixture preparation time will be reduced, which may lead to undesirably high PM emission. Optimization of combustion characteristics, such as those for keeping a higher heat release rate and cumulative heat release, occurrence of the start of combustion of nearby TDC, 50% of heat release of nearby TDC, and lower combustion duration, are important for engine operation with less PM emission. Because a diesel engine’s PM emission is lower with a lean fuel-air mixture, lean burn is an effective technology to reduce the emission. Therefore, the important parameters for PM reduction include increased premixed charge, high oxygen level, high mixture preparation time, high in-cylinder temperature, lean burn, and combustion phase optimization.
Reciprocating Engines
Published in Neil Petchers, Combined Heating, Cooling & Power Handbook: Technologies & Applications, 2020
Depending on the air-fuel ratio used, engines may be classified as lean-burn, stoichiometric, or rich-burn. The ratio of oxygen (or air) to fuel that produces perfect combustion is referred to as the stoichiometric air-fuel ratio. If more oxygen (excess air) is used in the combustion process cycle, the engine is referred to as a lean-burn engine. If fuel intake is equivalent to or greater than the stoichiometric quantity, the engine is referred to as a rich-burn engine. Diesel engines always operate with lean air-fuel ratios and under part-load, operate with extremely lean air-fuel ratios. Spark-ignited engines may be designed to operate over a wide range of air-fuel ratios, from rich to very lean.
Review on performance and emission of spark ignition engine using exhaust gas recirculation
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Chandrakumar Pardhi, Rabindra Prasad, C.P. Jawahar, Sanjay Chhalotre, Zafar Said
Hot EGR appears to be helpful toward full loads, while cool EGR appears to be useful at lower loads. (Talei, Jafarmadar, and Khalilarya 2020) carried out an experimental work to investigate a combustion system’s capabilities well before introducing an EGR system. Because of lower combustion product temperatures and a slight increase in CO emissions, employing early-combustion and cooled EGR in a lean-burn engine reduces NOx emissions from 8.82 g/kWh to 4.40 g/kWh (a 50-percentage reduction) while not affecting CO2 emissions. Furthermore, Unburnt hydrocarbon emissions decreased within a limited range of cooled EGR but escalated beyond this range due to incomplete combustion. Furthermore, the results revealed that boosting cold EGR reduced the prechamber engine’s fundamental parameters, such as work done in a full cycle. According to the findings, for every 5% increment in cold EGR, the engine output power drops by about 0.2 kW (3–4%), and the efficiency drops slightly (less than 1%).
Numerical study of turbulent jet ignition process at different injection strategies in a single-cylinder engine with active pre-chamber
Published in Combustion Science and Technology, 2022
Xiao Li, Lijia Zhong, Lei Zhou, Ming Jia, Haiqiao Wei
With the intensification of the fossil energy crisis and stringent emission regulations, improving the thermal efficiency of internal combustion engines has become an urgent issue in recent years. A lean-burn engine with excess air can effectively enhance thermal efficiency and reduces NOx emissions due to the higher specific heat ratio and reduced heat loss at a lower combustion temperature (Li et al. 2010; Ning et al. 2020; Talei, Jafarmadar, Khalilarya 2020). However, ignition stability and flame propagation have poor performance as the fuel-air mixture becomes leaner. Turbulent jet ignition, which can ensure ignition reliability and increase the flame propagation speed, is a promising method in the lean-burn engine (Gentz, Gholamisheeri, Toulson 2017; Peters et al. 2020; Stadler et al. 2019).
Numerical simulation of combustion characteristics and emission predictions of methane-air and hydrogen-air mixtures in a constant volume combustion chamber using multi-point laser-induced spark ignition
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Prashant Mahadev Patane, Milankumar Ramakant Nandgaonkar
The increasing concern toward climate change and environmental degradation imposes tightening of emission legislations to the transportation sector worldwide. Thus to satisfy this emission legislation and continue the quest to enhance engine performance motivates researchers to explore alternative fuels and develop a new ignition and combustion technology. Several alternative fuels, such as compressed natural gas (CNG), hydrogen, ethanol, biodiesel and liquefied petroleum gas (LPG), etc., have been investigated and are promising alternative fuels. The lean-burn combustion using higher spark energy will increase thermal efficiency and reduces heat transfer, exhaust emissions, mainly NOx, and knocking tendency (Weinrotter et al. 2005a). However, there are many issues in burning lean mixtures like incomplete combustion, sluggish flame propagation (Lamoureux, Djebaili-Chaumeix, and Paillard 2003), increase in cyclic variation, and intermittent flame failure (Weinrotter et al. 2005a). These issues can result in decreased power output, efficiency, and increased emissions (Karim, Wierzba, and Al-Alousi 1996).