• Energy Research

This paper reports the study of a conceptual gasoline Internal Combustion Engine (ICE) using scroll type rotary device rather than conventional piston as the main engine component. The proposed innovate engine adopts Humphrey Cycle to maximize the power performance of ICE. A performance comparison of the Humphrey Cycle, Otto cycle and Brayton cycle has firstly been conducted and studied. The effects of using different designed compression ratio under variable expansion ratio have been investigated, which identify the optimal operational conditions under different compression/expansion ratio of the engine. A case study has been conducted to study the performance of small scale scroll-type rotary ICE. Results pointed out under designed compression ratio from 2:1 to 10:,1 the effective energy efficiency of the scroll-type rotary ICE ranges from 0.41 to 0.55 and the effective power from the system ranges from 2.88 to 15.82 kW.

The relationship between fuel compositions and particulate matter (PM) emissions originating from a gasoline direct injection (GDI) engine was explored and used to identify optimal fuel composition for minimizing the number concentrations of both nucleation mode and accumulation mode PM via a predictive PM model developed by using optimum mixture design DoE (Design of Experiments). N-octane, isooctane, xylene and ethanol, were blended to form test fuels according to the DoE design, and the solid Particle Number (PN) emissions were measured by a particle spectrometer DMS500. The responses for the DoE design were the nucleation mode PN and accumulation mode PN. The results indicated that aromatics produced more PN emissions, whilst the effects of other fuel components on the PN emissions were unclear because of the interactive effect arising from different combinations of fuel substances. Two non-linear mathematic models for both modes PN were validated experimentally according to ANOVA analysis.

The formation and evolution of the initial spray structure of diesel fuel in the near-nozzle region under different injection and ambient pressures were studied. A visualisation experiment study on diesel fuel using long-distance microscopy and nanosecond-pulse flashlight was performed. Four types of spray tip structure were identified and named as ‘needle’, ‘bubble’, ‘mushroom’ and ‘umbrella’. The obtained high-resolution images revealed that both injection pressure and ambient pressure had a significant influence on the evolution of the spray tip structure. The measurement of the spray penetration and spray angle showed that the increase of injection pressure enhanced spray dispersion while the increase of ambient pressure exhibited an opposite effect. In order to provide a better understanding on the formation mechanism, a numerical study based on large eddy simulation (LES) and volume of fluid (VOF) interface capturing technique was conducted.

The macroscopic characteristics of Hydrotreated vegetable oil (HVO), a renewable biodiesel, were investigated by both experimental and numerical approaches in this paper. The experiment on spray of 0.6ms injection duration was conducted in a constant volume vessel (CVV) at 1800 bar common rail pressure, 70 bar ambient pressure and 100℃ ambient temperature, and the numerical work with the Wave breakup model and RNG k-ε turbulence model was done on a corresponding 2D geometric model at the same condition. The results indicated that the spray tip penetration grew with a decreasing tip velocity and the cone angle increased gradually after a dramatic growth and slight drop. Moreover, the prediction of numerical method, when used in conjunction with experimental studies, was proven effective in elucidating the macroscopic characteristics of HVO spray. The error between the predicted spray tip penetration and the experimental one was no more than 4% except that within 0.2ms flow time after SOI. In addition, the predicted cone angle was in similar trend to the experimental one and the error was within 10% after 0.2 ms.

In this paper, validated simulations using Ricardo WAVE have been performed to investigate the effect of the Miller cycle and low-carbon fuels on the performance (power, torque, BTE and BSFC) and emissions of a diesel engine. The results show that the increased Miller cycle effect (larger deviation of the advanced or retarded intake valve closing from the standard intake valve closing time) will decrease NOx, CO and HC emissions, and slightly improve brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC) with slight loss in engine performance and increase in soot emissions. An engine running B0 (diesel with 0% Biodiesel in the blend) with a −18% Miller cycle effect has a reduction in NOx of 9% and CO of 4.3% with a decrease of 1.6% in power at the rated engine speed. Using low carbon fuels drastically reduces emissions with reduced BTE and increased BSFC. When used in conjunction, the Miller cycle and low-carbon fuels have an improved effect on both performance and emissions. The optimal results demonstrate that using B60 (60% Biodiesel in the blend) and a −8% Miller effect contributes to a 1.5% improvement in power, 1.2% in BTE, 13.3% in NOx, 38.5% in CO, 8.9% in HC, and 33.0% in soot at a cost of 6.0% increase in BSFC. The results show that it is an easy way to reduce NOx, CO, HC and soot emissions and increase the BTE of the engine by combining Miller cycle and low-carbon fuels.

The main macroscopic characteristics of Hydrotreated Vegetable Oil (HVO) spray in both injection and post-injection periods are investigated via computational fluid dynamics (CFD) in this research. A 2D CFD work employing the Wave breakup model and the KHRT breakup model are validated by the experimental data from a Constant Volume Vessel (CVV). Spray tip penetration and cone angle are obtained by the CFD model under various conditions, where the rail pressure, fuel temperature, ambient pressure and ambient temperature are independently varying. Results demonstrate that the Wave model has overall higher precision in predicting the spray tip penetration and the average cone angle than the KHRT model. By the End of Injection (EOI), spray tip penetration is significantly increased by increasing rail pressure and decreasing ambient pressure. While the average cone angle is larger at high ambient pressure but not sensitive to rail pressure at the cold ambient condition. The average cone angle during injection can be enlarged by high ambient temperature, especially when the rail pressure is also high. Nevertheless, spray tip penetration can only be slightly promoted by high ambient temperature. Fuel temperature has no comparable impact on spray tip penetration and cone angle during injection. In the post-injection period (after the EOI), ambient temperature becomes dominant and spray tip penetration can be reduced by either ambient temperature or fuel temperature. An empirical model is also correlated via Design of Experiments (DoE) and has high precision in predicting spray tip penetration after the breakup time.