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Oxyfuel combustion and nitrogen-free combustion coupled with Carbon Capture and Storage (CCS) techniques have been recently proposed as an efficient method to achieve carbon free emissions and to improve the combustion efficiency in diesel engines. In this study, a 3-D computational fluid dynamics model has been used to evaluate the influence of oxyfuel-HCCI combustion on engine operating conditions and combustion characteristics in a HSDI diesel engine. Investigations have conducted using four different diluent strategies based on the volume fraction of pure oxygen and a diluent gas (carbon dioxide). The first series of investigations has performed at a constant fuel injection rating at which 4.4 mg of fuel has injected per cycle. In the second part of analysis, the engine speed was maintained at 1500 rev/min while the engine loads were varied by changing the fuel injection rates in the range of 2.8 to 5.2 mg/cycle.

A three-dimensional simulation was carried out for investigating effects of negative valve overlap (NVO) on gas exchange and fuel-air mixing processes in a diesel homogeneous charge compression ignition (HCCI) engine with early fuel injection. It was found that the case with longer NVO produced a stronger swirl motion and a more significant vortex below the intake valve due to the high annular jet flow through the valve curtain area during the intake stroke. However, there was not much difference in the values of swirl ratio, tumble ratio and turbulence intensity between different NVOs at the end of compression stroke. It was also seen that enlarged NVO not just increased in-cylinder temperature but also improved the temperature homogeneity. With increased NVO, there is a bigger spray shape and more droplets exist in gaps of sprays. This demonstrates that stronger turbulence intensity and higher temperature homogeneity with higher NVO improve fuel vaporization and air-fuel mixing.

Droplet velocities in a diesel fuel spray before and after impinging on a wall as well as air movement around the spray are measured at room temperature and pressure. The range of fuel injection pressure is from 101 MPa to 139 MPa. The diagnostic equipment is a Laser Doppler Velocimetry with Burst Spectrum Analyzer (LDV-BSA).The results show that the droplet velocities of such a high pressure diesel fuel spray spread in a wide range (about 0-250m/s), so it is necessary to use the ensemble average for describing the velocity variation with time and space. After injection, the velocity reaches its peak value rapidly then attenuates gradually. When the spray impinges on the wall, the average velocity of the rebounded droplets is obviously reduced and the rebounded angle of most droplets is smaller than 30 degree when the incident angle is 70 degree. In the near field zone, the air entrainment in spray jet appears to be lower than that in gaseous one.

Using a Laser Doppler Velocimetry with Burst Spectrum Analyzer (LDV-BSA), droplet velocities of a diesel fuel spray under a pressure higher than 100 MPa were measured at different points within the spray profile. Results show that although the mean velocity distribution at the sampling plane is rather uniform, the number-based droplet velocity distributions of two sampling points at the same plane are different. The conclusions agree with theoretical predictions through maximum entropy principle qualitatively.

As the impacts of global warming have become increasingly severe, Oxy-Fuel Combustion (OFC) has been widely considered as a promising solution to reduce Carbon Dioxide (CO2) for achieving net-zero emissions. In this study, a one-dimensional simulation was carried out to study the implementation of OFC technology on a practical turbocharged 4-cylinder Gasoline Direct Injection (GDI) engine with economical oxygen-fuel ratios and commercial gasoline. When the engine is converted from Conventional Air-fuel Combustion (CAC) mode to OFC mode, and the throttle opening, oxygen mass fraction, stoichiometric air-fuel ratio (lambda = 1) are kept constant, it was demonstrated that compared to CAC mode, θF gets a remarkable extension whereas θC is hardly affected. θF and θC are very sensitive to the ignition timing, and Brake Specific Fuel Consumption (BSFC) would benefit significantly from applying Maximum Brake Torque (MBT) ignition timing.