guang Li

Experimental study of the spray characteristics of biodiesel based on inedible oil

We studied the spray characteristics of inedible oil using experimental and simulation methods. Spray penetration, spray cone angle and spray tip speed were measured at different biodiesel ratios in a constant volume vessel with wide visualization and high back pressure, using a high-speed camera. The characteristics of biodiesel spray were simulated under the same conditions using Star-CD software. The experimental results showed that, as the ratio of biodiesel in the blends increased, spray penetration and spray speed increased, but the spray cone angle decreased. Throughout the spray injection period, the region at 0.05-0.475S (spray tip penetration) was a key area affecting spray cone angle. From 0.8 ms after injection, the spray penetration deviation ratios started to increase with increasing biodiesel blend ratios. Simulation results showed similar macroscopic spray characteristics to the experimental results for jatropha oil. The results also showed that the Sauter mean diameter of blend fuels was greater than that of diesel, and spray was more concentrated, due to the higher viscosity and surface tension of the biodiesel, compared with conventional diesel fuel. The macroscopic and microscopic spray properties of blended fuels containing 5%, 10% and 20% biodiesel were similar to diesel.

Experimental study of the effect of water injection on the cycle performance of an internal-combustion Rankine cycle engine

The internal-combustion Rankine cycle engine uses pure oxygen instead of air as the oxidant during the combustion process so as to preclude the creation of nitrogen oxide emissions. Carbon dioxide can be recovered from the water vapour–carbon dioxide exhaust gas mixture through condensation at a relatively low cost and, thus, an ultra-low-emission working cycle is achieved. In this paper the working process of the internal-combustion Rankine cycle was studied on the basis of bench tests on a prototype engine. An oxygen–carbon dioxide mixture was utilized to simulate exhaust gas recirculation in order to control the combustion process, and water was injected near top dead centre to determine the impact on the reaction rate and the cycle performance. The results demonstrated that water injected at a temperature of 120 °C can modulate the reaction rate and expand the area of the pressure–volume diagram through vaporization. Furthermore, combustion phasing is retarded without reducing the maximum cylinder pressure. The indicated work under the test conditions is increased by 7.8%. However, when the water-injection temperature is 20 °C, the cycle performance is reduced.

Study on characteristics of controllable active thermo-atmosphere of a vitiated coflow combustor

Turbulent combustion remains to be one of most complicated technologies due to the complexities of turbulence and combustion as well as the interaction of both. This paper presents a vitiated coflow combustor, which is newly used for the fundamental research into turbulent combustion. The characteristics of controllable active thermo-atmosphere (CATA) of a vitiated coflow combustor are investigated. The results show that the oxygen mole fraction of vitiated coflow flames between 0% and 21% yield coflow temperature between 700 and 1500 K, and there is a constant temperature space as a cylinder with a radius of 40 mm. These features of the vitiated coflow indicate the existence of a controllable active thermo-atmosphere, which benefits the basic study on the autoignition of a combustible mixture in a homogeneous charge compression ignition (HCCI) combustion.

Method of ion current detection for HCCI combustion on SI/HCCI dual mode engine

With the advantages of high thermal efficiency and extra low NOx and soot emissions, homogeneous charge compression ignition (HCCI) combustion has become a promising combustion method. Comparing with the SI engine or diesel engine, it is hardly to control combustion phase and combustion period on a HCCI engine directly. Hence, sensing of combustion phase and combustion state is very important for HCCI engine control. In this paper a method of detecting ion current signal as the feedback of combustion characters was discussed through a series of experiments on a gasoline HCCI engine. When the engine operated in pure HCCI mode, the ion current was measured and several parameters were abstracted from ion current waveform in order to investigate the relationship between the ion current and the combustion characters. Simultaneously, the in-cylinder pressure was measured and the rate of heat release was calculated. Experiment results show that there is a strong correction between HCCI combustion phasing and ion current signal. On the other hand, the relationship between ion current and combustion phasing was also discussed when the engine operated under spark assisted HCCI mode. Thus through a set of parameter definition the influence of ignition coil discharge to ion current also be researched.

A Method of Torque Estimation Utilizing Ionization Sensing Technology in Internal Combustion SI Engines

This paper describes a method of torque estimation by using in-cylinder ionization sensing technique in a internal combustion SI engine. Through the characterization of the ion current signal measured across the spark plug electrode with four parameters, two peaks of ionization signal were investigated and used to build the relationship between the net torque of engine and the ion current signal. From the experiment results, a conclusion can be drawn that the averaged ionization signal over 20 consecutive combustion cycles is well correlative with the variation of torque, especially in the case of higher torque conditions. The intensity and position of the second peak of this signal are most sensitive to the change of torque.

In-cycle combustion feedback control for abnormal combustion based on digital ion current signal:

For better stability of ion current employed for in-cycle combustion diagnosis and feedback control, this research develops a digital post-processing unit for in-cylinder ion current signals. Based on the processed digital ion current signal, abnormal combustion in gasoline direct injection engine is successfully detected, and the in-cycle remedy feedback control is achieved as well. Both re-ignition and re-injection are utilized for misfiring remedy, and only re-injection is employed for knocking inhibition. The accuracy of misfiring diagnosis is achieved no less than 94%, and the re-injection combined with re-ignition operation is shown to be feasible for misfiring remedy as well. The accuracy of knocking diagnosis is around 85% (knocking rate = 20%). The re-injection under the pre-knocking condition is shown to be effective for knocking inhibition.

Multi-Coil High Frequency Spark Ignition to Extend Diluted Combustion Limits

A reliable ignition process is desirable for the ignition of a lean and/or EGR diluted cylinder charge commonly adopted to achieve clean and efficient engine combustion. In this work, ignition of a diluted propane-air mixture is investigated using a high energy spark ignition system. Efforts are dedicated towards development of a novel ignition system that improves the ignition quality whilst keeping within the bounds of current spark ignition hardware to facilitate potential application in future clean combustion engines. A multi-coil ignition system was developed to adjust the spark energy and the discharge pattern. With enhanced primary voltage up to 120 V, a multi-spark strategy with frequency up to 20 kHz can be implemented. The combustion visualization results show that the application of both multi-coil and multi-spark strategy can promote the flame propagation. The high frequency multi-spark strategy shows better ignition quality compared to a single-spark strategy. With discharge energy enhancement by coupling more coils, the ignition success rate is increased under diluted mixture conditions. The diluted combustion limits are therefore extended with the help of these spark strategies.

An Ultra-High Power Ignition System for EGR-Diluted GDI Engine

An innovative ignition system was evaluated for its suitability for EGR-diluted GDI engine. The energy measurements showed the ultra-high power ignition system could provide about 12 kW power and generated a strong shock wave captured by a high-speed photography. The 2000 r/min@0.44 MPa BMEP engine test showed a 10% EGR ratio limit extension and the enhanced flame kernel and flame propagation helped to raise the thermal efficiency by 5.5% relatively.

Development and Application of Dual UniValve System Based on a GDI Engine with SI/HCCI Dual Combustion Modes

A full-variable-valvetrain prototype named Dual UniValve System has been developed for a GDI engine with SI/HCCI dual combustion modes, improving the fuel economy and emission performance under some of part and low load conditions. Based on the dynamic performance test, reliability of Dual UniValve System has been qualified. In addition, under the NEDC condition, UniValve system can optimize the friction loss significantly. The switching response time between valvelifts of 0–8 mm is only 0.16 s, which provides a fast response for transient conditions. Furthermore, in the engine test with Dual UniValve System, SI/HCCI combustion mode switching has been also achieved with a fast speed, which increased indicated efficiency by 10 % and reduced NOX emissions by 99 %.

Simulation and experimental study on ion current under GDI-HCCI combustion mode

For a gasoline HCCI engine, the major challenge comes from the ignition and combustion control. Therefore, a feedback signal is necessary to detect combustion state and to realise closed-loop control of combustion process, and ionisation technology was studied for the purpose. The simulation results indicated that the 3D-CFD model could accurately predict in-cylinder pressure, heat release rate, ion profile, ion distribution and its generation mechanism. The experimental results showed that the fuel injection rate in NVO was of more significance to the HCCI combustion phase and the ion current, and HCCI combustion phase can be controlled by the fuel transmutation. In the wake of the excess air coefficient reducing, the amplitudes of the cylinder pressure and ion current were increased, and the phases were advanced. Under high load condition, the reduction of the throttle percentage caused increase in the fluctuation of the IMEP coefficient but weakness in the middle load.