Experimental and numerical study the effect of combustion chamber shapes on combustion and emissions characteristics in a heavy-duty lean burn SI natural gas engine coupled with detail combustion mechanism

Abstract Lean burn natural gas engines offer low particulate emissions than diesel counterparts and provides higher efficiency when compared to stoichiometric operation. However, with the lean burn strategy, three-way catalysts (TWC) compatibility is lost due to the oxidized exhaust stream. In comparison, the exhaust gas recirculation (EGR) dilution strategy can maintain compatibility with emission after-treatment systems. The maximum tolerated EGR levels are limited by the combustion stability degradation resulting from unfavorable mixture gas composition. Prechamber spark ignition (PCSI) systems, known to increase dilution tolerance in SI engines under lean conditions, was evaluated as a means to improve EGR dilution tolerance. Scavenging of residuals within the pre-chamber is typically a concern with these systems and as such studies on these systems working with various levels of EGR ratios are rare. In this work, an unscavenged (or unfueled, or passive) PCSI system installed in a medium-duty natural gas engine is modeled using CONVERGE CFD code. Simulation results are compared against the experimental data in terms of in-cylinder pressure and heat release rates from low to high (10% to 22%) EGR levels. The prediction capability of two combustion models, a multi-zone well-stirred reactor model and a flamelet-based combustion model, i.e. G-equation, are compared and evaluated under these conditions within the RANS framework. The G-equation model predictions agreed well with experiments up to 18.8% EGR dilution level. In comparison, the MZ-WSR model predicted slow prechamber combustion at all dilution levels which influenced the main chamber combustion phasing.

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The Effect Mechanisms of Intake Manifold Water Injection on the Emissions of a Natural Gas Engine

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/943/1/012015 ◽

2021 ◽

Vol 943 (1) ◽

pp. 012015

Author(s):

Qichao Qin ◽

Youpeng Chen ◽

Zhuogeng Qin ◽

Chaoqun Tu

Keyword(s):

Natural Gas ◽

Water Injection ◽

Experimental System ◽

Intake Manifold ◽

Combustion Mechanism ◽

Lean Burn ◽

Energy Of Combustion ◽

Oh Groups ◽

Gas Engine ◽

Natural Gas Engine

Abstract NOx is the main emission of lean burn natural gas engine (NGE). Water injection (WI) is an effective method to reduce NOx, which has been widely studied in conventional fuel engine. Currently, there are few researches on the application of WI in NGE. The influences of WI on NGE are not clear. In the paper, the effect mechanisms of WI on the emissions of NGE are studied. Based on the thermodynamic properties of water and the combustion mechanism of natural gas, the emissions generation mechanism of NGE with WI was analyzed. According to the experimental system, the effects of intake manifold water injection (IMWI) on the emissions of a lean burn NGE was carried out. The results show that, with WI, the in-cylinder temperature decreased greatly, which effectively inhibited the formation of thermal NO. Water generated a lot of OH groups, which effectively inhibited the formation of rapid NO. At 1800 rpm and 0.92g/s WI rate, NOx is reduced by 70.4%. OH group could effectively promote CO oxidize to CO2. At 1000 rpm and 0.92g/s WI rate, CO is decreased by 22.2%. However, since the decrease of the total activation energy of combustion reaction, the chain breaking reaction increased, resulting in a significant increase in HC. At 800rpm and 0.92g/s WI rate, HC was increased by 11.6%.

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