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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Numerical Analysis of Biogas Composition Effects on Combustion Parameters and Emissions in Biogas Fueled HCCI Engines for Power Generation

[+] Author and Article Information
Iván D. Bedoya

Grupo de Ciencia y Tecnología del Gas y Uso Racional de la Energía,
Department of Mechanical Engineering,
University of Antioquia,
Medellín, Colombia
e-mail: ibedoyac@udea.edu.co

Samveg Saxena

Combustion Analysis Laboratory,
University of California Berkeley,
Berkeley, CA 94720
e-mail: samveg@berkeley.edu

Francisco J. Cadavid

Grupo de Ciencia y Tecnología del Gas y Uso Racional de la Energía,
Department of Mechanical Engineering,
University of Antioquia,
Medellín, Colombia
e-mail: fcadavid@udea.edu.co

Robert W. Dibble

Combustion Analysis Laboratory,
University of California,
Berkeley, CA 94720
e-mail: rdibble@berkeley.edu

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 11, 2012; final manuscript received February 3, 2013; published online June 12, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(7), 071503 (Jun 12, 2013) (7 pages) Paper No: GTP-12-1438; doi: 10.1115/1.4023612 History: Received November 16, 2012; Revised February 03, 2013

This study investigates the effects of biogas composition on combustion stability for a purely biogas fueled homogeneous charge compression ignition (HCCI) engine. Biogas is one of the most promising renewable fuels for combined heat and power systems driven by internal combustion engines. However, the high content of CO2 in biogas composition leads to low thermal efficiencies in spark ignited and dual fuel compression ignited engines. The study is divided into two parts: First experimental results on a biogas-fueled HCCI engine are used to illustrate the effects of intake conditions on combustion stability, and second a simulation methodology is used to investigate how biogas composition impacts combustion stability at constant intake conditions. Experimental analysis of a four cylinder, 1.9 L Volkswagen TDI diesel engine shows that biogas-HCCI combustion exhibits high gross indicated mean effective pressure (close to 8 bar), high gross indicated efficiency (close to 45%), and ultralow NOx emissions below the US2010 limit (0.27 g/kWh). An inlet absolute pressure of 2 bar and inlet temperature of 473 K (200 °C) were required for allowing HCCI combustion with a biogas composition of 60% CH4 and 40% CO2 on a volumetric basis. However, slight changes in inlet pressure and temperature caused large changes in cycle-to-cycle variations at low equivalence ratios and large changes in ringing intensity at high equivalence ratios. Numerical analysis of biogas-HCCI combustion is carried out with a sequential methodology that includes one-zone model simulations, computational fluid dynamics (CFD) analysis, and 12-zones model simulations. Numerical results for varied biogas composition show that at high load limit, higher contents of CH4 in biogas composition allow advanced combustion and increased burning rates of the biogas air mixture. Higher contents of CO2 in biogas composition allow lowered ringing intensities with moderate decrease in the indicated efficiency and power output. NOx emissions are not highly affected by biogas composition, while CO and unburned hydrocarbons (HC) emissions tend to increase with higher contents of CO2. According with the numerical results, biogas composition is an effective strategy to control the onset of combustion and combustion phasing of HCCI engines running biogas, allowing more stabilized combustion at low equivalence ratios and safe operation at high equivalence ratios. The main advantages of using biogas-fueled HCCI engines in CHP systems are the low sensitivity of power output and indicated efficiency to biogas composition, as well as the ultralow NOx emissions achieved for all tested compositions.

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References

Figures

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Fig. 1

Ringing intensity for different combustion phasing (CA50), intake pressures and intake temperatures

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Fig. 2

Normalized standard deviation of IMEPg for different combustion phasing (CA50), intake pressures and intake temperatures

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Fig. 3

Brief description of the sequential methodology

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Fig. 4

(a) In-cylinder average temperature predicted with the 12-zone model for different biogas compositions. (b) In-cylinder average heat capacity ratio (Cp/Cv ratio) for biogas-air mixture predicted with Fluent 6.3 at motored conditions and multiple biogas compositions.

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Fig. 5

(a) In-cylinder H2O2 molar fraction predicted with the 12-zone reduced in zone 12 for multiple biogas compositions. (b) In-cylinder average pressure traces predicted with the 12-zone reduced model for multiple biogas compositions.

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Fig. 6

Onset of combustion (CA10), combustion phasing (CA50), and burn duration (10–90% of CHR) calculated with the 12-zone reduced model as a function of biogas composition

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Fig. 7

Gross indicted efficiency, ringing intensity, and IMEPg calculated with the 12-zone reduced model as a function of biogas composition

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Fig. 8

Hydrocarbon (HC), carbon monoxide (CO), and nitric oxides (NOx) emissions calculated with the 12-zone reduced model at exhaust valve open (EVO) as a function of biogas composition

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