An Assessment of Hydrogen Addition to Methane Combustion with Argon as a Working Fluid in a Constant Volume Combustion Chamber

ABSTRACT

Combustion of natural gas in combination with hydrogen, coupled with argon as a working fluid, is a promising approach to increasing the efficiency of internal combustion engines while decreasing emissions. The use of argon as a working fluid effectively eradicates NOx, extends the flammability limits, and increases the thermal efficiency due to its high specific heat ratio. Additionally, the hydrogen addition aids in emissions reduction and enhances the flammability range. In this study, premixed CH₄-H₂-O₂-Ar combustion is experimentally investigated in an optically accessible constant volume combustion chamber to determine the effect of hydrogen addition on laminar burning velocity, flame morphological structure, and instabilities when argon replaces nitrogen as the working fluid. A numerical thermodynamic model is applied to calculate the laminar burning velocity and an image processing technique is used to quantify the flame speed. The experiments show that, in comparison to methane alone, the addition of hydrogen (40%) to the mixture at atmospheric pressure (1 bar) and room temperature (298 K) increases the maximum laminar burning velocity by 37%, increases the maximum flame speed by 35%, and extends the lower and upper flammability limits from equivalence ratio of 0.4 to 0.3 and 1.6 to 1.7, respectively.

KEYWORDS:

• Methane-hydrogen combustion
• argon
• laminar burning velocity
• flame speed
• flammability limit
• constant volume combustion chamber

Nomenclature

α	=	Hydrogen composition in the fuel mixture
γ	=	Specific heat ratio
δ	=	Displacement thickness
$\delta { }^{\mathrm{\prime }}$	=	Integration variable related to displacement thickness
η	=	Thermal efficiency
${\rho }_u^{\mathrm{\infty }}$	=	Density of unburned gas that is far from the boundary layer
Φ	=	Equivalence ratio
A	=	Wall area
$A_b$	=	Area of burned gas
b	=	Burned gases
CVCC	=	Constant volume combustion chamber
e	=	Specific internal energy
$E_i$	=	Total initial energy
IC	=	Internal combustion
$m_i$	=	Total initial mass of the gaseous mixture
${\dot{m}}_b$	=	Mass burning rate
P	=	Pressure
$P_i$	=	Initial pressure
r	=	Compression ratio
$r_0$	=	Radius of the CVCC
$r_f$	=	Flame radius
$S_u$	=	Laminar burning velocity
$S_b$	=	Flame speed
$SI$	=	Spark-ignited
t	=	Time
$T_i$	=	Initial temperature
u	=	Unburned gases
$v_b$	=	Specific volume of burned gases
$v_u$	=	Specific volume of unburned gases
$x$	=	Mass fraction of the burned gas
$x{ }^{\mathrm{\prime }}$	=	Integration variable related to mass fraction

Highlights

• Replacing N₂ with Ar increases the S_u and S_b of CH₄-H₂ combustion.

• Use of Ar as a working fluid extends the lower & upper flammability limits of CH_4.

• Inclusion of H₂ and Ar affects the morphological structure of CH₄ flames.

Acknowledgments

This material is based upon work supported by Columbia Gas of Massachusetts under award #29797 with the University of Massachusetts Lowell.

Additional information

Funding

This work was supported by the Columbia Gas of Massachusetts [29797].