On the Fuel Spray Transition to Dense Fluid Mixing at Reciprocating Engine Conditions

Abstract

This paper presents a theoretical and experimental study of direct fuel injection at conditions relevant to spark ignition (SI) and compression ignition (CI) engines. The focus of this work is to identify the conditions under which fuel droplet formation should occur or be suppressed. An experimental investigation of the injection of sub- and supercritical propane into gaseous nitrogen is first discussed. This includes study of one case in which the fuel remained supercritical with respect to temperature and pressure throughout the injection event, and which appears to be the first time that truly supercritical hydrocarbon fuel injection is examined experimentally. A nondimensional parameter τ representing the ratio of the time scales of droplet formation and droplet evaporation is also proposed and used to explain the observed occurrence or suppression of fuel droplets at different conditions. While instants of τ < 1 suggest that droplets should always be observed in any plausible SI or CI engine design, τ > 1 also occurs during the bulk delivery of heavier hydrocarbons in CI engines. In such cases, this should justify simplified modeling of the spray as a dense fluid that mixes with its surroundings, ignoring droplet transport during the less important parts of the injection event.

Examination of diesel spray combustion in supercritical ambient fluid using large-eddy simulations

“…Various experiments have been performed under Engine Combustion Network 1 (ECN) Spray A [2][3][4][5][6][7][8] and Spray D [9][10][11][12][13][14][15][16][17][18] target conditions in order to contribute to the understanding of diesel combustion. In addition, Reynolds-Averaged Navier-Stokes (RANS) and largeeddy simulations (LES) have been used to simulate Spray A [19][20][21][22][23][24][25][26][27][28][29][30][31] and Spray D 15,[32][33][34] in computational investigations.…”

A multispectral, extinction-based diagnostic for drop sizing in optically dense diesel sprays

“…Despite recent advances in the field, mechanisms governing high-pressure atomization are not well understood. 4 This is largely due to the experimental and computational challenges associated with resolving multi-scale, highly turbulent flows, particularly in the near-nozzle region, that is, up to 100 orifice diameters away from the injector tip. However, such fundamental knowledge is crucial for developing predictive models for engine design.…”

Large eddy simulations of diesel-fuel injection and auto-ignition at transcritical conditions

“…This generalized framework provides a theoretical foundation to better understand and model the fuel injection interfacial transition dynamics in regions above the fluid critical condition. More recently, Poursadegh et al (2017) conducted both experimental and theoretical analysis to show that under typical Diesel-engine relevant conditions, the time scale for heating up the jet by surroundings is much shorter than the jet breakup time scale, which explains the turbulent mixing behaviour observed in experiments. To provide insights into the high-pressure combustion systems, accurate and robust simulation tools are required.…”

“…The dynamics of the interfacial forces were shown to gradually decrease as the interface broadens once it enters the continuum regime. Poursadegh et al 5 performed experimental and theoretical investigations to show that under typical operating conditions, relevant to diesel engines, the time scale for the heating of the liquid jet by its surrounding is much shorter than the jet breakup time scale, explaining the turbulent mixing behavior observed in experiments.…”