Autoignition delay time measurements were recorded for blends of CH4/n-C4H10 in “air” at pressures of approximately 10, 16, 20, 25, and 30 atm from fuel-lean to fuel-rich conditions at two different fuel compositions, 90% CH4/10% n-C4H10 and 70% CH4/30% n-C4H10, and temperatures from 660 to 1330 K in both a rapid compression machine and a shock-tube facility. A detailed chemical kinetic model consisting of 1328 reactions involving 230 species was validated using the ignition delay data from this study. This mechanism has already been used to simulate previously published ignition delay times over a wide range of conditions. It was found that the model quantitatively reproduces the ignition delays from both rapid compression and reflected shock waves, accurately capturing reactivity as a function of the temperature, pressure, equivalence ratio, and fuel composition.

The International Marine Organization (IMO) has a goal of reaching 40% reduction of GHG emissions by 2030 and target of a full 50% reduction in marine fleet wide GHG emissions by 2050, while other organizations and governments desire to develop a path to Net-Zero GHG emissions by no later than 2050. To accomplish this, engines with near zero GHG emissions must be developed now. In addition to new ships, there is a large existing fleet of diesel fueled engines in the market today which are candidates for retrofit. Ammonia fueling of a diesel engine using dual-fuel combustion represents a viable zero-carbon fuel and combustion strategy suitable for long-haul / heavy-duty transportation due to its favorable storage properties of liquid at low tank pressure. The challenge, however, is ammonia is hard to ignite, slow to burn, and cool when it does burn which creates a significant challenge from a combustion point of view. Conventional dual fuel (CDF) will not be able to burn more than 50% NH3-Diesel ratios efficiently with acceptable combustion quality, thus, combustion enhancement is required to get ammonia to ignite and burn at higher substitution rates. Woodward has developed a fueling and combustion control strategy using diesel pilot injection as the ignition source and combustion accelerant. And using RCCI combustion (Reactivity Controlled Compression Ignition) controlled by Active Combustion Control (ACC) high ammonia-diesel substitution ratios (GSR) is demonstrated to burn as fast or faster than the baseline diesel. With the proportional reduction of carbon in the fuel and an appropriate ammonia slip catalytic technology, it is demonstrated that ammonia can be used as a GHG reduction fuel in dual-fuel diesel engines which can contribute to reduction in GHG emissions proportional to the NH3 substitution ratio. This is a technology which can be deployed today on both retrofit of existing engines as well as on new engines to meet the marine fleet average GHG emissions goals.

Purpose -An axisymmetric shock-tube model of the high-pressure shock-tube facility at the Texas A&M University has been developed. The shock tube is non-conventional with a non-uniform cross-section and features a driver section with a smaller diameter than the driven section. The paper aims to discuss these issues. Design/methodology/approach -Computations were carried out based on the finite volume approach and the AUSM þ flux-differencing scheme. The adaptive mesh refinement algorithm was applied to the time-dependent flow fields to accurately capture and resolve the shock and contact discontinuities as well as the very fine scales associated with the viscous effects. The incorporation of a conjugate heat transfer model enhanced the credibility of the results. Findings -The shock-tube model is validated with simulation of the bifurcation phenomenon and with experimental data. The model is shown to be capable of accurately simulating the shock and expansion wave propagations and reflections as well as the flow non-uniformities behind the reflected shock wave as a result of reflected shock/boundary layer interaction or bifurcation. The pressure profiles behind the reflected shock wave agree with the experimental results. Originality/value -This paper presents one of the first studies to model the entire flow field history of a non-uniform diameter shock tube with a conjugate heat transfer model beginning from the bursting of the diaphragm while simultaneously resolving the fine features of the reflected shock-boundary layer interaction and the post-shock region near the end-wall, at conditions useful for chemical kinetics experiments. An important discovery from this study is the possible existence of hot spots in the end-wall region that could lead to early non-homogeneous ignition events. More experimental and numerical work is needed to quantify the hot spots.

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Results from a heterogeneous shock-tube approach recently demonstrated at Texas A&M University, wherein a hydrocarbon fuel is introduced in liquid phase with gaseous oxidizer, are presented. The shock tube has been designed for controlled measurement of ignition delay times, sooting phenomena, radical species concentrations, time-dependent species profiles, and nanoparticle-aided combustion using heavy hydrocarbons which are difficult to study using the traditional shock tube approach. Aerosol is generated in a high-vacuum manifold positioned 4-m from the endwall where optical and pressure-based diagnostics are stationed. The approach reduces the propensity for fuel-film deposition near the endwall avoiding optical and/or kinetic disturbances that could result. The aerosol enters the shock tube initially as a two-phase flow of liquid fuel and gaseous oxidizer/inert gas. Liquid droplets partially evaporate while resident in the shock tube, prior to shock wave generation, and are then completely vaporized behind the incident shock wave. Behind the reflected shock wave, then, resides a pure gas-phase fuel and oxidizer mixture. The primary benefit of the aerosol shock tube approach is the ability to inject fuels of low vapor pressure at high or low concentrations. The classic shock-tube approach introduces gas-phase constituents only, and has difficulty accommodating low vapor-pressure liquids, except when component partial pressures are much lower than what is usually required. In the present work, n-heptane aerosol (C7H16, Pvap, 20 °C ∼ 35 torr), was generated with O2/Ar carrier gas and dispersed in the shock tube in a uniform manner. Stoichiometric ignition delay times with temperature varied from 1240 K to 1600 K and pressure maintained near 2.0 atm are compared to gas-phase data at similar conditions and a chemical kinetic model for heptane combustion. Excellent agreement was found between the two-phase aerosol approach and the classical method involving vapor-phase n-heptane and pre-mixed gases. The measured activation energy for the stoichiometric mixture at 2.0 atm (EA = 42.3 kcal /mol), obtained with the two-phase technique, compares well with the literature value.