The effect of high-pressure injection variations on the mixing state of underexpanded methane jets

Abstract

This work presents a joint experimental and numerical study of global characteristics and mixing behavior of underexpanded methane jets at high-pressure conditions in a Constant Volume Chamber. Injection pressures of 200, 250, and 300 bar and pressure ratios of 4, 5, 6, 8, and 10 at each of those pressures have been investigated. Tracer LIF with acetone as tracer has been applied to experimentally quantify the mixing of methane and quiescent air. In order to exploit the symmetry of the configuration, accompanying simulations have been carried out in Reynolds-Averaged Navier-Stokes framework with the k – w SST turbulence model and real-gas modelling based on the Soave-Redlich-Kwong Equation of State has been employed to account for high-pressure corrections in thermodynamic and caloric properties. The experiments confirm the hyperbolic decay of axial fuel concentration and the Gaussian shape of traverse concentration profiles in the self-similar region of the jets, while simulation results match well with experimentally determined fuel concentration fields. It is found that scaling laws proposed in literature for steady-state jet propagation can qualitatively interpret the effect of injection variations on jet tip penetration and volume. Increasing pressure ratio at fixed injection pressure leads to the formation of slightly richer jets, with slightly smaller mass percentage in the range of air-to-fuel ratios most favorable to autoignition. By contrast, increasing pressure ratio at fixed chamber pressure leads to virtually identical Probability Distribution Functions of local air-to-fuel ratios and the same is observed when employing a fixed pressure ratio at higher pressure levels.

Visualization and comparison of methane and hydrogen jet dynamics using schlieren imaging

“…At choked flow conditions, the pressure ratio is the most dominant parameter affecting the mass flow [20]. In addition, higher pressure ratios can lead to higher turbulence levels and faster mixing [40] which are particularly influential for direct injection engines. In this study, the effect of pressure ratio on the jet characteristics both by changing P i at a constant P ch and by changing P ch at a constant P i is investigated.…”

Impact of a split injection strategy on mixing, ignition and combustion behavior in Premixed charge compression ignition combustion

“…The quantitative interpretation of the processed tracer PLIF images as equivalence ratio fields relies on the procedures outlined in [26,34,35]. The interpretation of measured tracer PLIF intensities as equivalence ratio Φ is governed by the following equation…”

“…The bulk piston temperature 𝑇𝑇 as well as the air density 𝜌𝜌 air at each time step are calculated from measured piston pressures 𝑝𝑝 in assuming adiabatic compression/expansion. In assuming rotational symmetry of the fuel spray, the proportionality constant 𝐾𝐾 links the injected fuel mass to the volume integrated intensity and is used to transform the quantum yield corrected fluorescence intensity to local fuel density [34,35]. The operation inherently assumes a low tracer concentration so that absorption of laser energy can be neglected and that the excitation energy of the probed transition stays below the saturation limit.…”

Experimental Study on Entrainment Characteristics of High-Pressure Methane Free Jet

“…The high-pressure NG has its own characteristics. Sakellarakis et al conducted both experimental and numerical simulation research studies of high-pressure methane jets, and the results confirmed the hyperbolic decay of axial fuel concentration and the Gaussian shape of traverse concentration profiles in the self-similar region of the jets. Cheng et al investigated the turbulent plasma jet and reported that the mass flow rate of the ambient air entrained into the turbulent plasma jet is comparatively large and almost directly proportional to the mass flow rate at the jet inlet.…”