Han Wu

• Ph.D.
• Lecturer at Beijing Institute of Technology

There are few studies on the effect of turbulent jets on the combustion characteristics of passive pre-chamber (PC) gasoline engines, and their mechanism needs to be elucidated. Therefore, a 3-D simulation was performed using CONVERGE software. The results reveal that a modest expansion in the PC volume contributes to combustion due to the increase...

The wall combustion is one of the soot and unburned hydrocarbon formation sources in the engine cylinders, which is affected by both spray and wall parameters. The impingement dynamics of the droplets on liquid films have been widely studied. However, there is less focus on the droplet impingements on hot liquid film, which is more representative a...

To clarify the mechanism of destructive knock combustion and piston ablation in heavy-duty diesel engines operating at low temperatures, CONVERGE simulation and wall temperature measurement were performed. The results show that as the initial temperature (intake valve closing instant) decreases from 380K to 307K, the spray wet-wall ratio increases...

The chemical reactions of each component of hydrocarbon fuels at low temperatures become more complex and the interactions become stronger, which is considered to potentially affect the soot formation characteristics. A 0-dimensional simulation was applied to analysis the component coupling effect on polycyclic aromatic hydrocarbon(PAH) forming pro...

The effect of injection pressure on diesel ignition has been widely studied, but the conclusions are different or even contradictory. Thus, the 3-D simulation was conducted at injection pressures of 40–280 MPa under different spray wet-wall conditions. The results show that as the injection pressure increases, the fuel injection ends earlier, so th...

Given a lack of clarity on fuel-attached combustion and its effect on the wall heat load in diesel engines remain to be clarified. Therefore, visualization and wall temperature measurement experiments are carried out in a constant volume combustion chamber, while CONVERGE simulation is performed to make further explanation. The fuel film attached t...

The multiple-injection strategies can significantly improve the diesel engine startability at low-temperature conditions, but the processes are extremely complex due to the effect of various factors simultaneously. To find out how the pilot injection affects the main injection, the spray and ignition with different injection strategies at low tempe...

The two-stroke rod-less opposed pistons engine provides a new possibility to improve the energy conversion path by optimizing cam profile. Constrained by the optimization algorithms and profile control equations, previous research could not optimize the profile with a high-degree freedom under practical engine operating conditions. A thermodynamic...

The combustion of wall-impinging diesel spray of heavy-duty diesel engines deteriorates combustion quality under cold-start conditions, making it difficult to control soot emissions. To investigate the causes of soot increase in the combustion of wall-impinging spray at low temperature and low speed starting conditions, the effect of the starting f...

For diesel engines, the distance between the wall and the spray nozzle is an important feature for the matching of spray and combustion chamber geometry. In this study, the effects of the cold wall with different wall distance on the spray and ignition characteristics at low-temperature conditions are systematically analyzed. CFD simulations are us...

Spherically expanding flames of TRF/air mixtures diluted with different levels of CO2 content at elevated temperatures and pressures were experimentally studied in this work to clarify the effects of exhaust gas recirculation (EGR), especially the effects of CO2 in EGR gases on the laminar flame characteristics of gasoline fuel. The experiments hav...

The effect of diesel engine continuous strengthening on combustion and emission remains to be clarified. This study tested combustion and emission processes at different intake pressures on a single-cylinder diesel engine. The results show that the combustion of diesel engine after continuous strengthening is concentrated in diffusion and post-comb...

The knock combustion and pollutant emission of heavy-duty diesel engines at low temperatures are still unclear, especially under different injection timings. Therefore, this study illustrates the above issues through CONVERGE simulation. The results show that with the start of injection (SOI) sweeps from −7°CA to −32°CA, a large amount of liquid-ph...

Two-stroke engines have higher power density than traditional four-stroke engines, and therefore are suitable for engine downsizing. In this work, a four-stroke single-cylinder diesel engine is modified for two-stroke operation, and the combustion system is designed and optimized using a 3D simulation. Three different combustion chamber profiles an...

Diesel engines show poor performance and high emissions under cold-start conditions. The intake manifold burner is an effective method to increase the intake air temperature and improve engine performance. In this paper, a visualization system was employed to investigate the combustion process of the intake manifold burner. The effects of diesel fl...

The difference in impinging ignition characteristics of light- to heavy-duty diesel engines at low temperatures and the heating effect of fuel film combustion on the wall are still not well understood. Thus, visualization experiments are conducted in a constant volume combustion chamber using Mie-scattering and direct photography methods, and 3-D s...

While electrification of light duty vehicles is becoming a real solution to abate local pollutant as well as greenhouse gases emission, heavy duty applications (such as long distance, freight and maritime transport) will keep requiring fuel-based propulsion systems. In these sectors, dominated by compression ignition engines, research on alternativ...

The entrainment coefficient reflects the air-fuel mixing quality, which is one of the foremost concerns for the development of cleaner and higher power-density internal combustion engines. Previous prediction models constructed by the change of axial mass flow rate have lower accuracy under high injection pressure conditions. During modeling in the...

Diesel engines play an important role in road transportation. However, they are facing strict regulations in reducing soot and harmful substances emissions. Ducted fuel injection (DFI) is a new method that effectively attenuates soot on a large scale. How this technology reduces emissions by boosting spray atomization remains unknown. This study fo...

The impinging spray ignition has been widely studied, but the mechanism is unclear, especially at low temperatures. Thus, the 3-D simulation was conducted at ambient temperatures of 740–1200 K and wall temperature of 393 K. The results reveal that the fuel–air mixing and ignition processes of an impinging jet are approximately the same as that of a...

Wall-impinging ignition has been widely studied, but it is still poorly understood at low temperatures. Thus, visualization experiments are performed in a constant volume combustion chamber using direct photography methods. The results show that the injection pressure effect is highly sensitive to temperature, and increased injection pressure helps...

Featured Application This work proposes a newly designed single-piston miniature free-piston generator, which features simple configuration and better sealing. This device has promising applications as the power source for small-scale electrical equipment and portable devices. This work carried out the preliminary parametric study of its performanc...

The effect of wall temperature on the ignition of vapor-phase spray impingement has been studied extensively, but the mechanism of the liquid-phase case is not clear. Thus, the visualization experiment was conducted at wall temperatures of 363–673 K using Mie-scattering, shadowgraph, and direct photography methods in a constant volume combustion ve...

A comprehensive measurement and investigation of the cellularization of methanol/hydrogen flame is important for the thorough understanding of the transition of turbulent flame. In this work, a constant volume combustion bomb with schlieren photography technology is used to study the flame evolution of methanol/hydrogen fuel. By investigating the f...

It is a common sense that diesel engines produce worse soot emission than gasoline engines, even though gasoline direct injection also brings about terrible sooting tendency. However, reports showed that diesel emits less soot than gasoline in laminar diffusion flames, which implies that soot emission is a combined effect of multiple factors, such...

The effect of injection pressure on impinging ignition at low temperatures is not systematic or even confusing. This work is to reveal the impinging ignition mechanism by the numerical method to further improve the success rate and thermal efficiency at cold-start conditions in a diesel engine. In which, n-dodecane was used as the diesel surrogate,...

The wall-attached fuel layer of the combustor usually leads to an unstable combustion and produces an unexpected emission, such as aerosol particles and unburn hydrocarbons. In this study, the impaction of ethanol droplet on a heated liquid surface was examined for investigating the factors those could effectively control the fuel atomization and a...

Compressed natural gas-Diesel dual-fuel combustion mode, the partial replacement of diesel fuel with cleaner fuel, is one of the most important strategies to achieve clean efficient combustion. However, low substitutions conditions face unstable combustion and high emission issues. Thus, the current work investigated the effect of hydrogen blending...

Lean combustion can be a more effective method to enhance the thermal efficiency of diesel engine, while also face incomplete-combustion and long-combustion duration issues at ultra-lean conditions. Effects of hydrogen, known with wider flame limits and greater burning velocity, on lean burn limits and burning characteristics of n-heptane were stud...

Although engines fueled with diesel/gasoline blends show excellent combustion and emission performance, its low-temperature flame development characteristics under cold-start conditions remain to be further verified. To clarify the details, experiments were conducted in an optical constant volume combustion chamber using Mie-scattering and direct p...

Ducted fuel injection (DFI) is a cutting-edge technology for boosting the air-fuel mixture quality of heavy-duty diesel engines. The present study employs ducts with different lengths and inner diameters to investigate the diesel macroscopic spray characteristics of DFI spray by Schlieren optical technique and compares them with a free spray. The e...

Soot is one of the main pollutants produced by incomplete combustion of hydrocarbon fuels, which poses a serious threat to human health and the urban environment. Alcohols have been generally considered to be a potential clean fuel to reduce soot emissions. At present, alcohol fuels represented by methanol, ethanol, butanol and pentanol have been e...

Jet breakup during droplet impacted on heated surface has received wide concerns due to its regularity. The Weber number (We) is a common used dimensionless parameter to classify and analyze the phenomenon, but it is unable to summarize all detailed phenomenon variations and related theory. Thus, the effect of droplet size on jet breakup was invest...

Compressed natural gas/Diesel dual-fuel combustion mode, the partial replacement of diesel fuel with cleaner fuel, is one of the most important strategies to achieve clean efficient combustion. Thus, the current work investigated the effect of various natural gas substitution ratios on the combustion and soot emission characteristics experimentally...

In the heavy-duty diesel engine, the unavoidable impinging spray and ignition during low-temperature ignition have a significant impact on engine performance. In this study, the effects of injection pressure on the impinging spray and ignition characteristics of the heavy-duty diesel engine with a 0.32 mm nozzle were measured visually in a constant...

Methanol has been regarded as a promising alternative fuel. However, the problem in cold start and the resulting high emissions consistently constrain the development of methanol engines. Meanwhile, blending hydrogen in methanol has the potential to alleviate the above problem. Effects of blending hydrogen on the laminar flames of methanol under ch...

Cold start ability is essential for heavy duty vehicles equipped diesel engine operating in cold regions. However, it is the diesel jet’s initial flame developing characteristics that determines whether it is able to start success. Thus, it is investigated on a constant volume chamber by optical diagnostics technologies. In order to simulate cold s...

The effect of hydrogen addition on the methanol laminar flames under various pressures was investigated experimentally and kinetically. A constant volume chamber was used to perform the experiments. The flame propagation was recorded by a schlieren system and a high-speed camera. The CHEMKIN was used to calculate the detailed reaction process. The...

The effects of hydrogen addition on laminar premixed methanol–air flames were studied both experimentally and numerically. To achieve this, a constant volume chamber (CVC) and the premix code in CHEMKIN were used. During the experiments, the equivalence ratios (ϕ) and hydrogen mole fractions (Xh) were set to 0.6 to 1.8 and 0%–100%, respectively. In...

The study of hydrogen-air premixed flame propagation behavior and induced accelerated combustion in a constrained environment is of great significance for realizing rapid controllable combustion and promoting the efficient use of hydrogen energy. In this work, the propagation process of hydrogen-air premixed flame and the effect of different initia...

Micro-explosion has been concerned for decades due to its potential effect on fuel atomization and combustion. In this work, the characteristics of sputtering and micro-explosion induced by water-diesel emulsion fuel droplets impact on a heated surface under different water content (from 5% to 20% with an interval of 2.5%) and surface temperature c...

The performance of kerosene spray from an air-assisted system was investigated in a constant volume chamber by backlit imaging and shadowgraph technologies over various chamber pressures, temperatures, and fuel amount. The results show that the penetration decreases with the increase in the chamber pressures from 0.5 bar to 3.5 bar due to the reduc...

Impingement is a typical phenomenon occurring in diesel engine under cold start conditions. In this paper, the ignition and combustion characteristics of wall-impinging diesel spray under different wall conditions were investigated by using the high-speed photography, Mie scattering and Schlieren method on a constant volume chamber. It is found tha...

The evaluation of soot tendency of gasoline surrogates in simple atmosphere environments is essential for understanding soot formation processes and developing accurate soot models to represent real fuel chemistry in CFD simulations of gasoline engines. In this work, several surrogates were evaluated based on soot precursors and soot characteristic...

The impact of ethane (C2H6) addition to ignition delay of dimethyl ether (DME) under high-temperature conditions is opposite to that of other small molecule alkanes, but the trend is still unclear under low-temperature conditions. Thus, ignition delays of DME/C2H6 mixtures (C2H6 blending ratio ranging from 0% to 70%) were measured at temperatures o...

In view of the importance of atomization, droplet breakup induced by high Weber number and vapor bubble during droplet impacting onto a solid and heated surface has been studied extensively, but the understand on jet break-up phenomenon in the film boiling regime is still lacking. Thus, the work is trying to study the dynamic of jet break-up of n-b...

Gasoline addition in diesel fuel could not only improve the overall energy efficiency, but also could reduce the soot emission on diesel engine. However, the influence of gasoline on the soot forming characteristics has not been revealed fundamentally. A liquid burner system, modified from a Gülder burner, was applied to create strict laminar diffu...

Alcohols have been regarded able to reduce particulate emissions from GDI engines, which in turn requires a deeper understanding of the effect of fuel chemistry on the formation and growth of PAHs. This work focused on combustion and soot forming progress, thus studied the distribution characteristics of PAHs with different ring sizes by PLIF and t...

Characterization of soot formation is becoming more important for gasoline surrogate fuels, requiring a deeper understanding of the effect of toluene ratio on PAHs formation. In this work, the different size PAHs distribution in laminar diffusion flames was measured by PLIF technique, and the chemiluminescences of OH and CH radicals were recorded b...

Acetone–Butanol–Ethanol (ABE), as a clean and economical alternative transportation fuel, its component ratio has been reported impact spray combustion characteristics significantly. To fundamentally clarify the interactions between components in ABE, the laminar flame speeds (LFS) and stretch effect of ABE mixtures with component ratios (6:3:1, 3:...

Effect of turbulent jet ignition induced by pre-chamber sparkplug (PCSP), a simper version of turbulent jet ignition pre-chamber system without fuel injection, on the air-hydrogen combustion characteristics was conducted based on an optical constant volume chamber under varied equivalence ratio conditions. The dynamic pressure sensor and schlieren...

Alcohols are widely used to reduce soot emission as alternative fuel for SI engines. 2-D soot distribution of alcohols/gasoline blends were studied in laminar diffusion flames by 2C-LII technique. The results showed that the soot volume fraction decrease with alcohols blending ratio significantly. At the same blending ratio, the soot reducing abili...

Bio-butanol has been considered to be an important alternative fuel to reduce soot emissions from gasoline engines, and it has the potential to overcome the disadvantages brought by low-carbon alcohols. In this study, the effect of n-butanol addition on soot formation in gasoline laminar diffusion flame is investigated respectively under the same f...

Methanol has been considered to be a potential alternative fuel to reduce soot emissions from GDI engine. In order to fully understand the effect of methanol addition on soot formation, the 2-D distribution of soot volume fraction in methanol/gasoline laminar diffusion flames was measured quantitatively with two-color laser induced incandescence (T...

In view of the potential of bio-ethanol as an alternative fuel and the particulate matter (PM) issues during gasoline combustion , the soot distribution characteristics of ethanol-gasoline blends in laminar diffusion flames were studied on a Gülder liquid burner using the two-color laser induced incandescence (TC-LII) technique. During the experime...

The appearance of the squish flame is of great significance to accelerate burning progress and improve the combustion efficiency. In this paper, we experimentally studied the characteristics of the squish flame in a cylindrical constant volume vessel under different initial pressures and equivalence ratios by using high-speed schlieren photometry....

The diesel engine is widely regarded as a critical power source for transportation vehicles, construction machinery vehicles, and military-equipment due to its advantages of significant horse power, higher fuel efficiency, greater reliability. However, diesel engines do suffer from ignition issues in extremely cold environments. Ignition characteri...

Alcohols, especially n-butanol, have received a lot of attention as potential fuels and have shown to be a possible alternative to pure gasoline. The main issue preventing butanol’s use in modern engines is its relatively high cost of production. ABE, the intermediate product in the ABE fermentation process for producing bio-butanol, is being studi...

Acetone-butanol-ethanol (ABE), as the intermediate product during producing biobutanol by fermentation, is considered as a promising alternative fuel due to its advanced properties and lower recovery cost. The spray and combustion process of ABE20 (20% ABE and 80% diesel) and pure diesel was investigated in a constant volume chamber. The tested amb...