scholarly journals Effects of equivalence ratio variations on turbulent flame speed in lean methane/air mixtures under lean-burn natural gas engine operating conditions

2017 ◽  
Vol 36 (3) ◽  
pp. 3423-3430 ◽  
Author(s):  
Zhiyan Wang ◽  
Emmanuel Motheau ◽  
John Abraham
Keyword(s):  
Natural Gas ◽  
Equivalence Ratio ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Operating Conditions ◽  
Lean Burn ◽  
Gas Engine ◽  
Natural Gas Engine ◽  
Turbulent Flame Speed

Flame Characteristics and Turbulent Flame Speeds of Turbulent, High-Pressure, Lean Premixed Methane/Air Flames

2005 ◽  
Author(s):  
P. Griebel ◽  
R. Bombach ◽  
A. Inauen ◽  
R. Scha¨ren ◽  
S. Schenker ◽  
...  
Keyword(s):  
Flame Front ◽  
Gas Turbines ◽  
Equivalence Ratio ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Operating Conditions ◽  
Turbulent Flame Speed ◽  
Front Position ◽  
Preheating Temperature ◽  
Lean Premixed

The present experimental study focuses on flame characteristics and turbulent flame speeds of lean premixed flames typical for stationary gas turbines. Measurements were performed in a generic combustor at a preheating temperature of 673 K, pressures up to 14.4 bars (absolute), a bulk velocity of 40 m/s, and an equivalence ratio in the range of 0.43–0.56. Turbulence intensities and integral length scales were measured in an isothermal flow field with Particle Image Velocimetry (PIV). The turbulence intensity (u′) and the integral length scale (LT) at the combustor inlet were varied using turbulence grids with different blockage ratios and different hole diameters. The position, shape, and fluctuation of the flame front were characterized by a statistical analysis of Planar Laser Induced Fluorescence images of the OH radical (OH-PLIF). Turbulent flame speeds were calculated and their dependence on operating conditions (p, φ) and turbulence quantities (u′, LT) are discussed and compared to correlations from literature. No influence of pressure on the most probable flame front position or on the turbulent flame speed was observed. As expected, the equivalence ratio had a strong influence on the most probable flame front position, the spatial flame front fluctuation, and the turbulent flame speed. Decreasing the equivalence ratio results in a shift of the flame front position farther downstream due to the lower fuel concentration and the lower adiabatic flame temperature and subsequently lower turbulent flame speed. Flames operated at leaner equivalence ratios show a broader spatial fluctuation as the lean blow-out limit is approached and therefore are more susceptible to flow disturbances. In addition, because of a lower turbulent flame speed these flames stabilize farther downstream in a region with higher velocity fluctuations. This increases the fluctuation of the flame front. Flames with higher turbulence quantities (u′, LT) in the vicinity of the combustor inlet exhibited a shorter length and a higher calculated flame speed. An enhanced turbulent heat and mass transport from the recirculation zone to the flame root location due to an intensified mixing which might increase the preheating temperature or the radical concentration is believed to be the reason for that.

Combustion Analysis of a Natural Gas Engine

2003 ◽  
Author(s):  
Seref Soylu
Keyword(s):  
Natural Gas ◽  
Burning Rate ◽  
Equivalence Ratio ◽  
Operating Conditions ◽  
Engine Fuel ◽  
Ignition Timing ◽  
Gas Engine ◽  
Natural Gas Engine ◽  
Rate Analysis ◽  
Propagation Period

A two-zone thermodynamic model was developed for a spark ignition natural gas engine. The model was used to calculate instantaneous mass burning rate and thermodynamic state of burned and unburned zones of the combustion chamber content. Cylinder pressure data was collected at various engine operating conditions. Natural gas and natural gas–propane mixtures were used as engine fuel. From the burning rate analysis various combustion characteristics, such as flame initiation period (FIP) and flame propagation period (FPP) were calculated at various engine operating conditions. It was observed that both the FIP and FPP decrease with increasing equivalence ratio for lean mixtures. While the retarded timing decreases the FIP, the FPP has a tendency to increase. Addition of propane to natural gas reduces the FPP although the FIP is not affected. Unburned and burned gas temperatures are significantly raised with increase in equivalence ratio. However, ignition timing and propane fraction do not influence the temperatures as much as equivalence ratio does.

Experimental Examination of Prechamber Heat Release in a Large Bore Natural Gas Engine

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Daniel B. Olsen ◽  
Allan T. Kirkpatrick
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Equivalence Ratio ◽  
Dynamic Pressure ◽  
Pressure Rise ◽  
Main Chamber ◽  
Lean Burn ◽  
Gas Engine ◽  
Natural Gas Engine ◽  
Common Solution

A common solution in reducing NOx emissions to meet new emission regulations has been lean burn combustion. However, with very lean air∕fuel (A∕F) ratios, both carbon monoxide and hydrocarbon emissions become unacceptably high due to the spark misfiring and combustion instabilities. In order to mitigate this, a prechamber ignition system is often used to stabilize combustion at very lean A∕F ratios. In this paper, the heat release in a retrofit prechamber system installed on a large bore natural gas engine is examined. The heat release analysis is based on dynamic pressure measurements both in the main chamber and prechamber. The Woschni correlation is utilized to model heat transfer. Based on heat release modeling and test data analysis, the following observations are made. Main chamber heat release rates are much more rapid for prechamber ignition compared to spark ignition. During combustion in the prechamber, much of the fuel flows into the main chamber unreacted. About 52% of the mass in the prechamber, at ignition, flows into the main chamber during prechamber combustion. Prechamber total heat release, pressure rise, and maximum jet velocity all increase with increasing prechamber equivalence ratio. Prechamber combustion duration and coefficient of variation of peak pressure are minimized at a prechamber equivalence ratio of about 1.09.

Performance and Combustion Investigation of a Lean Burn Natural Gas Engine Using CFD

2018 ◽  
Author(s):  
Sridhar Sahoo ◽  
Srinibas Tripathy ◽  
Dhananjay Kumar Srivastava
Keyword(s):  
Natural Gas ◽  
Equivalence Ratio ◽  
Spark Ignition Engine ◽  
Engine Fuel ◽  
Lean Burn ◽  
Gas Engine ◽  
Natural Gas Engine ◽  
Spark Timing ◽  
Combustion Duration ◽  
Wide Range

Natural gas is widely used in sequentially port fuel injection engine to meet stringent emission regulation. Lean burn operation is one of the ways to improve spark-ignition engine fuel economy. The instability in the combustion process of the lean burn engine is one of the major challenges for engine research. In this study, the performance and combustion characteristics of a lean burn sequential injection compressed natural gas (CNG) engine were investigated numerically using computational fluid dynamics (CFD) modeling over a wide range of air/fuel equivalence ratio. A detailed chemical kinetic mechanism was used for natural gas combustion along with laminar flame speed model to capture lean burn operating condition within the combustion chamber. Combustion pressure, indicated mean effective pressure (IMEP), and heat release were analyzed for performance analysis, whereas flame development angle (CA 10), combustion duration, thermal efficiency were taken for combustion analysis. The results show that on increasing air/fuel equivalence ratio at a given spark timing, IMEP decreases as the lean burn mixture produces less amount of gross power output due to insufficient available energy. Moreover, lower burning velocity characteristic of natural gas extends the combustion duration, where a substantial amount of total energy released after top dead center. It is also seen that optimum spark timing (MBT) for maximum IMEP advances with an increase in air/fuel equivalence ratio due to late ignition timing under lean burn condition. CFD model successfully captures the effect of dilution to illustrate the considerations to design future combustion engine for spark ignited natural gas engine.

Experimental Examination of Prechamber Heat Release in a Large Bore Natural Gas Engine

2007 ◽  
Author(s):  
Daniel B. Olsen ◽  
Allan T. Kirkpatrick
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Equivalence Ratio ◽  
Laminar Flame ◽  
Dynamic Pressure ◽  
Pressure Rise ◽  
Main Chamber ◽  
Lean Burn ◽  
Gas Engine ◽  
Natural Gas Engine

A common solution to reducing NOX emissions to meet new emissions regulations has been lean burn combustion. However, with very lean air/fuel (A/F) ratios, both carbon monoxide and hydrocarbon emissions become unacceptably high due to spark misfiring and combustion instabilities. In order to mitigate this, a prechamber ignition system is often used to stabilize combustion at very lean A/F ratios. In this paper, the heat release in a retrofit prechamber system installed on a large bore natural gas engine is examined. The heat release analysis is based on dynamic pressure measurements both in the main chamber and prechamber. The Woschni correlation is utilized to model heat transfer. Based on heat release modeling and test data analysis the following observations are made. Main chamber heat release rates are much more rapid for prechamber ignition compared to spark ignition. During combustion in the prechamber much of the fuel flows into the main chamber un-reacted. About 52% of the mass in the prechamber, at ignition, flows into the main chamber during prechamber combustion. Prechamber total heat release, pressure rise, and maximum jet velocity all increase with increasing prechamber equivalence ratio. Prechamber combustion duration and coefficient of variation of peak pressure are minimized at a prechamber equivalence ratio of about 1.09, which corresponds roughly to the equivalence ratio of highest laminar flame speed. The above performance optimum does not correspond to the equivalence ratio where the most prechamber energy is released.

Assessment of Turbulent Combustion Models for Simulating Pre-Chamber Ignition in a Natural Gas Engine

2021 ◽  
Author(s):  
Joohan Kim ◽  
Riccardo Scarcelli ◽  
Sibendu Som ◽  
Ashish Shah ◽  
Munidhar Biruduganti ◽  
...  
Keyword(s):  
Natural Gas ◽  
Turbulent Combustion ◽  
High Efficiency ◽  
Turbulent Flame ◽  
Spark Ignition ◽  
Cylinder Wall ◽  
Gas Engine ◽  
Natural Gas Engine ◽  
Combustion Models ◽  
Combustion Processes

Abstract Lean combustion in an internal combustion engine is a promising strategy to increase thermal efficiency by leveraging a more favorable specific heat ratio of the fresh mixture and simultaneously suppressing the heat losses to the cylinder wall. However, unstable ignition events and slow flame propagation at fuel-lean condition lead to high cycle-to-cycle variability and hence limit the high-efficiency engine operating range. Pre-chamber ignition is considered an effective concept to extend the lean operating limit, by providing spatially distributed ignition with multiple turbulent flame-jets and enabling faster combustion rate compared to the conventional spark ignition approach. From a numerical modeling perspective, to date, still the science base and available simulation tools are inadequate for understanding and predicting the combustion processes in pre-chamber ignited engines. In this paper, conceptually different RANS combustion models widely adopted in the engine modeling community were used to simulate the ignition and combustion processes in a medium-duty natural gas engine with a pre-chamber spark-ignition system. A flamelet-based turbulent combustion model, i.e., G-equation, and a multi-zone well-stirred reactor model were employed for the multi-dimensional study. Simulation results were compared with experimental data in terms of in-cylinder pressure and heat release rate. Finally, the analysis of the performance of the two models is carried out to highlight the strengths and limitations of the two formulations respectively.

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