A study on the liquid length and flame lift-off length for Hydrogenated Catalytic Biodiesel/Diesel blended fuel in a constant volume combustion chamber

( Zhixia He ),( Weiwei Shang ),( Qian Wang ),( Xianyin Leng ),( Wenjun Zhong ),( Jiawei Cao ),( Bei Li ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-

The spray and combustion process is the fundamental factors affecting performance and emission of diesel engine, while the physicochemical properties of the fuel directly determine the spray combustion characteristics. The renewable and clean alternative fuel, which showed great potential of energy saving and emission reduction, makes studying on the influence of fuel physicochemical properties on the spray combustion characteristics very essential. In this paper, the effects of fuel physical and chemical properties on the spray combustion characteristics of diesel engine were studied by using mixed fuel with the catalytic hydrogenation biodiesel and diesel in constant volume combustion chamber. The effects of fuel physicochemical properties on the liquid length (LL) under combustion and evaporation conditions were studied based on the laser Mie scattering technic. The results showed that the LL under combustion conditions is shorter than the LL under evaporation conditions, and the difference became little when the ambient density is higher. In addition, the LL under combustion conditions decreases with the increase of fuel density and ambient temperature, while the ambient oxygen concentration and injection pressure have little effect on the LL. By using laser Mie scattering technology and chemical fluorescence visualization method innovatively, the LL under combustion and lift-off flame (LOL) was studied simultaneously, studying the interaction between them showed that the combustion LL and LOL can be in a stable state simultaneously with the injection duration long enough. With the increase of ambient density and ambient temperature, the LOL and LL decreases, the influence of ambient temperature on the LOL is greater than the effect on the LL. For the conditions where the combustion LL is shorter than the LOL, there will be more interspace for the mixing of air and fuel, and the fuel vaporization has completed before the fuel reaches the combustion region. For the conditions where the LL is longer than the LOL, there will be an overlap between liquid phase and combustion flame. The flame and liquid phase will interact with each other at these conditions. The vaporization of the liquid fuel is enhanced by the heat of the combustion and the combustion rate is reduced by the vaporization cooling. In addition, with the increase of cetane number of fuel density, the difference between LOL and liquid length became smaller and the decrease of LOL is greater than the decrease of LL. The physical and chemical properties of fuel have little effect on the difference between LOL and LL, when the injection pressure is low and the ambient oxygen concentration is high.

Effect of String Cavitation and Initial Air Bubbles in Diesel Injector Tapered Nozzles on Subsequent Spray

( Genmiao Guo ),( Zhixia He ),( Zhou Chen ),( Shenxin Sun ),( Zhengyang Zhang ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-

Flow inside nozzles and atomization dynamics in vicinity of the nozzle were crucial to diesel spray and combustion. And the tapered nozzle have attracted the researchers’ attention in recent years because of the better flow characteristics without the geometry induced cavitation. This paper presented the experimental and numerical analysis of string cavitation and near - nozzle spray dynamics. The string cavitation flow transient characteristics inside the tapered nozzle with the movement of needle were obtained based on the high speed digital microscopic imaging technique. Simultaneously, the formation and compression of initial air bubbles at the SOI (Start-of-Injection), and the air suction after the EOI (End-of-Injection) were captured clearly. The study indicates that the string cavitation was the direct cause of the spray instability. The various spray structures were observed at different injection pressures and different injection cycles under the same injection pressure. They might contain a clear single mushroom, tail region and intact liquid column, or had a tail in front of the mushroom. Occasionally, it presented as a double-mushroom shape, or did not include a clear mushroom. The difference of spray patterns may be due to the residual air bubbles surviving from the last injection or sucking into the nozzle during the needle opening. In order to explain the various spray patterns, effects of air bubbles distribution on initial spray patterns at the start stages of injections were investigated in a single-hole injector with a combination of the LES (Large Eddy Simulation) method and VOF (Volume of Fluid) model. The study confirmed that various spray patterns were affected by the injection pressure and initial air bubbles.

Numerical investigation of dual-fuel direct injection on RCCI combustion performance at low load condition

Peng Jiang,Xu Liu,Lixuan Cao,Qian Wang,Zhixia He 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.9

A numerical study was performed to investigate the combustion characteristics of hydrogenated catalytic biodiesel (HCB)/gasoline reactivity controlled compression ignition (RCCI) with dual-fuel direct injection at low load condition. The results indicated that compared with the conventional port injection RCCI, the dual-fuel direct injection can effectively control the distribution of in-cylinder gasoline mixture and improve the incomplete combustion phenomenon. The delay of start of injection (SOI) of gasoline can weaken stratified combustion, shorten combustion duration, reduce combustion efficiency, decrease NOx emission and increase soot emission. In contrast, the delay of SOI of HCB can intensify stratified combustion, prolong combustion duration, increase combustion efficiency, increase NOx emission and reduce soot emission. Compared with gasoline injection timing, HCB injection timing has a more profound effect on combustion efficiency and indicated thermal efficiency. When HCB injection timing was in the range of -25° ATDC (after top dead center) to -20° ATDC and gasoline injection timing of -50° ATDC to -45°ATDC, the engine has a better performance, with the combustion efficiency about 94 %, the indicated thermal efficiency around 45 %, and the NOx and soot emissions in the original exhaust less than the limit value of Euro VI standard.

Effects of injection rate on combustion and emissions of a pilot ignited direct injection natural gas engine

Qian Wang,Changsheng Shao,Qing Liu,Zhourong Zhang,Zhixia He 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.4

Effects of Injection rates on combustion process and emissions of engines operating with directly injected natural gas and pilot diesel were numerically investigated. Injection rates of natural gas and diesel were investigated separately utilizing five types of injection rates. An impact factor was defined to present the effects of the initial and terminal injection rates of diesel and natural gas on the combustion and emissions more intuitionally. Based on the simulation results, cylinder pressure and temperature were more sensitive to terminal injection rates of pilot diesel than initial injection rates, and lower terminal injection rates of pilot diesel can achieve lower NO and Soot emission level. However, there is a trade-off between NO and Soot emissions affected by different natural gas injection rates. The impact factors of pilot diesel injection rates on pressure show a double-peak trend. However, the impact factors of natural gas injection rates on pressure show a single-peak trend.

Study on the combustion process and work capacity of a micro free-piston engine

Qian Wang,Liming Dai,Kai Wu,Jin Bai,Zhixia He 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.11

With the main idea of exploring combustion conditions and the work capacity of the micro free-piston engine, the study concern isvisualization work including Homogeneous charge compression ignition (HCCI) combustion in the micro-chamber. The initial freepistonvelocity was adjusted to achieve a wide range of compression ratio. The combustion characteristics, the piston motion and pressurevariations under different compression ratios were discussed. Results indicate that the critical combustion condition occurs when thecompression ratio rises to a certain degree. Two-stage combustion characteristics can be observed in micro HCCI combustion processeswith the fuel of the DME/oxygen mixture. The micro-chamber pressure increases with the increase of the compression ratio. The criticalpeak pressure of 5.4 MPa is obtained when the initial piston velocity reaches 15.0 m/s and the diameter and the length of the microchamberis 3 mm and 37 mm, respectively.

Experimental study on the gas jet characteristics of a diesel-piloted direct-injection natural gas engine

Peng Jiang,Xu Liu,Lixuan Cao,Qian Wang,Zhixia He 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.3

The natural gas (NG) jet characteristics of NG/diesel dual-fuel injection under different NG injection pressures and dual-fuel injection intervals were studied in a constant volume chamber. The schlieren images showed that the development of NG jet was restricted in both axial and radial directions by diesel spray under dual-fuel injection conditions. Consistently, dual-fuel injection reduced NG jet tip penetration, NG jet cone angle and NG jet volume, yet increased average fuel-air equivalent ratio, compared to NG single-fuel injection. The increase of NG injection pressure from 3 MPa to 5 MPa enhanced NG jet tip penetration and NG jet volume, yet decreased jet cone angle under both single-fuel and dual-fuel injection conditions. The negative effects of diesel spray on NG jet became gradually reduced with the increase of injection interval. When the injection interval was longer than 1.5 ms, NG jet characteristics were close to those under single-fuel conditions.