Experimental and numerical analysis for high intensity swirl based ultra-low emission flameless combustor operating with liquid fuels

Abstract

Flameless combustion offers many advantages over conventional combustion, particularly uniform temperature distribution and lower emissions. In this paper, a new strategy is proposed and adopted to scale up a burner operating in flameless combustion mode from a heat release density of 5.4 to 21 MW/m 3 (thermal input 21.5 -84.7 kW) with kerosene fuel. A swirl flow based configuration was adopted for air injection and pressure swirl type nozzle with an SMD 35-37 µm was used to inject the fuel. Initially, flameless combustion was stabilized for a thermal input of 21.5 kW ( =5.37 MW/m 3 ). Attempts were made to scale this combustor to higher intensities i.e. 10.2, 16.3 and 21.1 MW/m 3 . However, an increase in fuel flow rate led to incomplete combustion and accumulation of unburned fuel in the combustor. Two major difficulties were identified as possible reasons for unsustainable flameless combustion at the higher intensities (i) A constant spray cone angle and SMD increases the droplet number density (ii) Reactants dilution ratio ( ) decreased with increased thermal input. To solve these issues, a modified combustor configuration, aided by numerical computations was adopted, providing a chamfer near the outlet to increase the . Detailed experimental investigations showed that flameless combustion mode was achieved at high intensities with an evenly distributed reaction zone and temperature in the combustor at all heat intensities. The emissions of CO, NO x and HC for all heat intensities (Ф=1 -0.6) varied between 11 -41, 6 -19 and 0 -9 ppm, respectively.These emissions are well within the range of emissions from other flameless combustion systems reported in the literature. The acoustic emission levels were also observed to be reduced by 8-9 dB at all conditions.

Simulation of MILD combustion using Perfectly Stirred Reactor model

“…MILD combustion has been well defined in many previous studies [1][2][3][4][5][6][7], and it is characterized by a reactant temperature, T r , higher than the reactant mixtures autoignition temperature T ign , and the temperature rise in the combustor, ∆T = T p − T r , is smaller than T ign . The efficiency increases due to heat recirculation from the combustion products, and with reduced emissions since the maximum temperature is decreased as a result of dilution and more homogeneous reaction in the combustor [8][9][10][11][12][13].…”

Effect of CO2/N2 Dilution on Characteristics of Liquid Fuel Combustion in Flameless Combustion Mode

“…They observed a uniform thermal field in the furnace and no CO was found at the outlet of the furnace. Flameless combustion of liquid kerosene fuel is reported earlier by our research group for possible application in gas turbine applications (Reddy et al (2014(Reddy et al ( , 2015a(Reddy et al ( , 2013(Reddy et al ( , 2015b, Sharma et al (2017Sharma et al ( , 2018). High-intensity swirl generated through the tangential air injection helped create strong recirculation of hot combustion products and flameless combustion mode.…”

“…The location of the fuel injector is offset by 25 mm from the central axis of the combustor (Sharma et al (2018)). More details of the combustor geometry can be found in Reddy et al (2015a) and Sharma et al (2018). Details of air inlet diameters and exit diameters for different operating conditions of fuel injection pressures are summarized in Table 1.…”

Critical Issues of Chemical Kinetics in MILD Combustion

“…The MILD combustion has been successfully employed in furnaces and boilers, and it could be potentially used into many other applications, such as gas turbines, biogas burners, burners for hydrogen reformers, or for combined heat and power (CHP) units and engines (Levy et al, 2004;Riccius et al, 2005;Lückerath et al, 2008;Khalil and Gupta, 2011;Li et al, 2011;Reddy et al, 2015;Ho et al, 2016). In addition, MILD-oxyfuel combustion for coal combustions represents a subcategory of MILD processes with high potentiality to overcome problems relative to oxycombustion systems (Li et al, 2011.…”

“…MILD combustion relies on a strong recirculation of mass and sensible enthalpy by recycling the exhausted gases to dilute and simultaneously preheat fresh reactants (Wünning and Wünning, 1977;Katsuki and Hasegawa, 1998;Weber et al, 2000Weber et al, , 2005Tsuji et al, 2003;Cavaliere and de Joannon, 2004;Dally et al, 2004;Milani and Wünning, 2007;Khalil and Gupta, 2011;Saxena and Bedoya, 2013;Reddy et al, 2015). The intrinsic nature of the process is based on autoignition/fuel-ultra-lean kernels that increase in size while being transported by convection (Van Oijen, 2013;Minamoto and Swaminathan, 2015), imposed by high-turbulence exhausted gas recirculation fluid-dynamics patterns, thus defining a process with homogenous intensive parameters within the combustion chamber (Özdemir and Peters, 2001;Noor et al, 2013a;Sidey et al, 2014;Sidey and Mastorakos, 2015).…”