A molecular dynamics investigation on fuel vaporization and mixing characteristics under sub/supercritical conditions

Molecular dynamics simulation is performed to study the influence of environmental pressure on the mixing process. Based on the OPLS-AA full-atomic potential function, the "gas-liquid-gas" simulation box model is used to study the evaporation characteristics of n-heptane at different environmental conditions. The results show that compared with the subcritical environment, the nitrogen molecules in the supercritical condition can diffuse into the liquid phase region earlier, and the temperature of the liquid phase rise faster, and then a unified supercritical fluid could be formed. Based on the density profile, a ?gas-liquid-gas? interface thickness is defined and the interface thickness is widened as the ambient pressure increase, resulting in the conventional subcritical evaporation transition to turbulent mixing process.

Numerical Evaluation of Spray-Guided Glow Plug Assistance on Gasoline Compression Ignition During Cold Idle Operation in a Heavy-Duty Diesel Engine

Starting compression ignition engines under cold conditions is extremely challenging, due to insufficient fuel vaporization, heavy wall impingement, and low ignitability of the fuel. For gasoline compression ignition (GCI) combustion strategies, which offer the potential for an enhanced NOx-PM tradeoff with diesel-like fuel efficiency, robust ignition and combustion in very cold conditions pose a significant challenge due to the low reactivity of gasoline fuels. Based on the previous understanding of the spray, ignition and combustion processes for a GCI engine under cold conditions, this study focuses on investigating the cold combustion performance of a heavy-duty GCI engine with glow plug ignition assist. Glow plugs, commonly used for low temperature cold starts in diesel engines, are used to pre-heat a segment of the mixture to improve its ignitability. Here, CFD studies are carried out to explore the influence of a spray-guided glow plug on the spray and combustion behavior of a GCI engine under cold operating conditions. In a prior study, the underlying CFD model has been validated using experimental data from a six-cylinder, 15 L heavy-duty diesel engine operating with a compression ratio (CR) of 17.3 at a 600 rpm cold idle condition with RON92 E0 gasoline. The energy intensity required by the glow plug to deliver stable combustion isparametrically studied. The size and location of the glow plug are also parametrically varied to evaluate their effects on the combustion process. The influence of the glow plug on the in-cylinder mixture distribution and the ensuing combustion process is also investigated. In particular, the localized fuel spray distribution and mixture formation near the glow plug are examined. The results reveal that the glow plug enhances GCI combustion under cold idle conditions and that the spray-guided glow plug improves fuel vaporization, leading to a rich mixture near the glow plug and an enhancement of the combustion efficiency. In addition, the effectiveness of the glow plug at a low ambient temperature of 0°C and a 200 rpm cold start condition is evaluated. These simulations suggest that the glow plug can improve the cold start performance of a GCI engine.

Lean Fully Premixed Injection for Commercial Jet Engines: An Initial Design Study

This article presents the results of an initial design study for a lean fully premixed (LFP) injector for commercial jet engine. The operating point considered is that of an high overall pressure ratio, small core engine at take-off condition. To perform this feasibility study, multiple relevant constraints are taken into account. The three-unit fully premixed injector has been designed by utilizing numerical simulations. The first unit of the injector is intended to perform complete fuel vaporization through heat transfer from the compressed air to the liquid fuel via a compact onboard heat exchanger. The second unit is designed to ensure premixing of the fully evaporated fuel and the air. Finally, the third unit ensures additional premixing and stability of the premixed swirling flame. The autoignition challenge associated with the design of the LFP injector is discussed in this article. The computational modeling approach that was used to design the units of the LFP injector is presented.

Investigations on performance of diesel engine by varying injection timings with design modification on piston crown

Purpose Investigations are carried out with the aim of improving performance of a diesel engine with the design modification on piston crown to stimulate the uniform combustion by inducing turbulence in the incoming charge. Design/methodology/approach A stirrer is introduced at the top of the piston so as to inculcate more turbulence to the incoming charge by improving the rate of fuel vaporization. Whirling motion is created in the combustible mixture by providing rotating blades on the cavity/bowl of the reciprocating piston head. By putting a simple link mechanism, the oscillatory motion of connecting rod will rotate the blade by an angle of 60°. Findings The investigations are carried out with and without swirl piston at 17.5 compression ratio and 200 bar injection pressure by varying injection timings. Originality/value Finally, the result shows that by using the modified piston, nearly 3 per cent of efficiency increased and 31 per cent of NOx emissions are reduced compared to that of a normal piston with 80 per cent load at standard injection timing.

Emissions From a Diesel Engine Operating in a Dual-Fuel Mode Using Port-Fuel Injection of Heated Hydrous Ethanol

Aftermarket dual-fuel injection systems in diesel engines using hydrous ethanol as secondary fuel have been developed as a means to lower emissions from older diesel-powered equipment. However, our previous work has shown that the emissions benefits of currently available aftermarket intake fumigation injection systems can be inconsistent with manufacturer claims. Our current study evaluates a newly developed aftermarket dual-fuel system that incorporates a fuel heating system and port fuel injection (PFI). This paper describes an experimental investigation of engine-out emissions from a John Deere 4045HF475 Tier 2 engine with port injection of 180 proof (90% ethanol by volume) hydrous ethanol. The engine was retrofitted with a custom fuel heat exchanger to heat the hydrous ethanol to a range of 46–79 °C for helping to improve fuel vaporization in the intake port. PFI duration was controlled using engine speed and throttle position as inputs to achieve a desired fumigant energy fraction (FEF), defined as the amount of energy provided by the hydrous ethanol based on lower heating value (LHV) over the total fuel energy provided to the engine. Data was collected over a range of FEF with direct injected diesel for eight operating modes comparing heated versus unheated hydrous ethanol. Results of the study indicate that as FEF increases, NO emissions decrease, while NO2, CO, THC, and unburned ethanol emissions increase. In addition, it was found that preheating the ethanol using engine coolant prior to injection has little benefit on engine-out emissions. The work shows that the implemented aftermarket dual-fuel PFI system can achieve FEF rates up to 37% at low engine load while yielding modest benefits in emissions.

Emissions From a Diesel Engine Operating in a Dual-Fuel Mode Using Port-Fuel Injection of Heated Hydrous Ethanol

Aftermarket dual-fuel injection systems in diesel engines using hydrous ethanol have been developed as a means to lower emissions from older diesel-powered equipment. However, our previous work has shown that the emissions benefits of currently available aftermarket intake fumigation injection systems can be inconsistent with manufacturer claims. Our current study evaluates a newly developed aftermarket dual fuel system that incorporates a novel fuel heating system and port fuel injection (PFI). This paper describes an experimental investigation of engine-out emissions from a John Deere 4045HF475 Tier 2 engine with port injection of 180 proof (90% ethanol by volume) hydrous ethanol. The engine was retrofitted with a custom fuel heat exchanger to heat the hydrous ethanol to a range of 46–79°C for helping to improve fuel vaporization in the intake port. PFI duration was controlled using engine speed and throttle position as inputs to achieve a desired fumigant energy fraction (FEF), defined as the amount of energy provided by the hydrous ethanol based on lower heating value (LHV) over the total fuel energy provided to the engine. Data was collected over a range of FEF with direct injected diesel for eight operating modes comparing heated versus unheated hydrous ethanol. Results of the study indicate that as FEF increases, NO emissions decrease, while NO2, CO, THC, and ethanol emissions increase. In addition, it was found that preheating the ethanol using engine coolant prior to injection has little benefit on engine-out emissions. The work shows that the implemented aftermarket dual-fuel PFI system can achieve FEF rates up to 37% at low engine load while yielding modest benefits in emissions.