A Numerical Study on the Effects of EGR Dilution in a Pre-Chamber Ignited Natural Gas Engine

2021 ◽  
Author(s):  
Prasanna Chinnathambi ◽  
Joohan Kim ◽  
Riccardo Scarcelli ◽  
Sibendu Som ◽  
Ashish Shah ◽  
...  
Keyword(s):  
Natural Gas ◽  
Numerical Study ◽  
Equation Model ◽  
Combustion Stability ◽  
Combustion Model ◽  
Particulate Emissions ◽  
Reactor Model ◽  
Lean Burn ◽  
Gas Engine ◽  
Natural Gas Engine

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.

Measurements and Modelling of a Lean Burn Gas Engine

1996 ◽  
Vol 210 (6) ◽  
pp. 449-462 ◽  
Author(s):  
C R Stone ◽  
K J S Mentis ◽  
M Daragheh
Keyword(s):  
Natural Gas ◽  
High Efficiency ◽  
Combustion Model ◽  
Hydrocarbon Emissions ◽  
Combustion System ◽  
Lean Burn ◽  
Gas Engine ◽  
Natural Gas Engine ◽  
Brake Mean Effective Pressure ◽  
Pressure Maximum

Natural gas is an alternative fuel that has potential for low emissions and a high efficiency. This paper presents the experimental results and predictions from a computer simulation of a fast burn high compression ratio (FBHCR) combustion system intended for use in a lean burn natural gas engine. Comparisons are made between the FBHCR combustion system at two compression ratios, predictions made by a two-zone combustion model and measurements from the original combustion system, for the brake efficiency, brake mean effective pressure, maximum cylinder pressure and the brake specific NOx emissions. Experimental measurements of the unburnt hydrocarbon emissions, the burn duration and the cycle-by-cycle variations in combustion are also discussed from the original and fast burn combustion systems. The results show how the conflicting aims of low emissions and low fuel consumption can be satisfied using a lean burn combustion system. The computer predictions are shown to be reliable, and thus suitable for estimating the performance of other engine builds.

scholarly journals Comparison of primary and secondary particle formation from natural gas engine exhaust and of their volatility characteristics

2017 ◽  
Vol 17 (14) ◽  
pp. 8739-8755 ◽  
Author(s):  
Jenni Alanen ◽  
Pauli Simonen ◽  
Sanna Saarikoski ◽  
Hilkka Timonen ◽  
Oskari Kangasniemi ◽  
...  
Keyword(s):  
Air Quality ◽  
Natural Gas ◽  
Particulate Emissions ◽  
Engine Exhaust ◽  
Gas Engine ◽  
Secondary Aerosol ◽  
Formation Potential ◽  
Natural Gas Engine ◽  
Evaporation Temperature ◽  
Catalyst Temperature

Abstract. Natural gas usage in the traffic and energy production sectors is a growing trend worldwide; thus, an assessment of its effects on air quality, human health and climate is required. Engine exhaust is a source of primary particulate emissions and secondary aerosol precursors, which both contribute to air quality and can cause adverse health effects. Technologies, such as cleaner engines or fuels, that produce less primary and secondary aerosols could potentially significantly decrease atmospheric particle concentrations and their adverse effects. In this study, we used a potential aerosol mass (PAM) chamber to investigate the secondary aerosol formation potential of natural gas engine exhaust. The PAM chamber was used with a constant UV-light voltage, which resulted in relatively long equivalent atmospheric ages of 11 days at most. The studied retro-fitted natural gas engine exhaust was observed to form secondary aerosol. The mass of the total aged particles, i.e., particle mass measured downstream of the PAM chamber, was 6–268 times as high as the mass of the emitted primary exhaust particles. The secondary organic aerosol (SOA) formation potential was measured to be 9–20 mg kgfuel−1. The total aged particles mainly consisted of organic matter, nitrate, sulfate and ammonium, with the fractions depending on exhaust after-treatment and the engine parameters used. Also, the volatility, composition and concentration of the total aged particles were found to depend on the engine operating mode, catalyst temperature and catalyst type. For example, a high catalyst temperature promoted the formation of sulfate particles, whereas a low catalyst temperature promoted nitrate formation. However, in particular, the concentration of nitrate needed a long time to stabilize – more than half an hour – which complicated the conclusions but also indicates the sensitivity of nitrate measurements on experimental parameters such as emission source and system temperatures. Sulfate was measured to have the highest evaporation temperature, and nitrate had the lowest. The evaporation temperature of ammonium depended on the fractions of nitrate and sulfate in the particles. The average volatility of the total aged particles was measured to be lower than that of primary particles, indicating better stability of the aged natural gas engine-emitted aerosol in the atmosphere. According to the results of this study, the exhaust of a natural gas engine equipped with a catalyst forms secondary aerosol when the atmospheric ages in a PAM chamber are several days long. The secondary aerosol matter has different physical characteristics from those of primary particulate emissions.

Experimental study of combustion strategy for jet ignition on a natural gas engine

2020 ◽  
pp. 146808742097775
Author(s):  
Ziqing Zhao ◽  
Zhi Wang ◽  
Yunliang Qi ◽  
Kaiyuan Cai ◽  
Fubai Li
Keyword(s):  
Experimental Study ◽  
Natural Gas ◽  
Efficient Points ◽  
Lean Burn ◽  
Gas Engine ◽  
Absolute Value ◽  
Natural Gas Engines ◽  
Natural Gas Engine ◽  
Excess Air ◽  
Lean Limit

To explore a suitable combustion strategy for natural gas engines using jet ignition, lean burn with air dilution, stoichiometric burn with EGR dilution and lean burn with EGR dilution were investigated in a single-cylinder natural gas engine, and the performances of two kinds of jet ignition technology, passive jet ignition (PJI) and active jet ignition (AJI), were compared. In the study of lean burn with air dilution strategy, the results showed that AJI could extend the lean limit of excess air ratio (λ) to 2.1, which was significantly higher than PJI’s 1.6. In addition, the highest indicated thermal efficiency (ITE) of AJI was shown 2% (in absolute value) more than that of PJI. Although a decrease of NOx emission was observed with increasing λ in the air dilution strategy, THC and CO emissions increased. Stoichiometric burn with EGR was proved to be less effective, which can only be applied in a limited operation range and had less flexibility. However, in contrast to the strategy of stoichiometric burn with EGR, the strategy of lean burn with EGR showed a much better applicability, and the highest ITE could achieve 45%, which was even higher than that of lean burn with air dilution. Compared with the most efficient points of lean burn with pure air dilution, the lean burn with EGR dilution could reduce 78% THC under IMEP = 1.2 MPa and 12% CO under IMEP = 0.4 MPa. From an overall view of the combustion and emission performances under both low and high loads, the optimum λ would be from 1.4 to 1.6 for the strategy of lean burn with EGR dilution.

A Lean Burn Low Emissions Gas Engine for Co-Generation

1996 ◽  
Vol 210 (3) ◽  
pp. 203-211 ◽  
Author(s):  
K J S Mendis ◽  
C R Stone ◽  
N Ladommatos ◽  
M Daragheh
Keyword(s):  
Combustion Model ◽  
Hydrocarbon Emissions ◽  
Combustion System ◽  
High Compression Ratio ◽  
Specific Mass ◽  
Lean Burn ◽  
Gas Engine ◽  
Natural Gas Engine ◽  
System A ◽  
Brake Mean Effective Pressure

This paper presents the rationale behind a fast burn high compression ratio (FBHCR) combustion system intended for use in a lean burn natural gas engine. Comparisons are made between the FBHCR combustion system, predictions made by a two-zone combustion model and measurements from the original combustion system, for the brake efficiency, brake mean effective pressure and the brake specific NOx emissions. Experimental measurements of the unburnt hydrocarbon emissions, the burn duration and the cycle-by-cycle variations in combustion are also discussed from the two combustion systems. The results show how the conflicting aims of low emissions and low fuel consumption can be satisfied by using a lean burn combustion system. A comparison is also made between the following ways of expressing the exhaust emissions: volumetric, brake specific, mass per megajoule of fuel and gravimetric referenced to a specified oxygen level.

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