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One of the most important trends for advanced diesel engines is downsizing, i.e., higher power density, which means more fuel is burned in a shorter period. In order to achieve rapid combustion for a high-power density diesel engine, the effects of bowl shape, diameter-to-depth ratio of bowl, and arrangement of nozzle holes on combustion and performance were investigated by CFD simulation. The effects of four bowl shapes, two of which were double-layer split bowls (DLSBs), as well as four diameter-to-depth ratios and three arrangements of nozzle holes were numerically assessed. The results show that the DLSB with a shallow dish-like structure yielded a remarkable effect of swirling flow by fuel splitting into upper- and lower-layer zones, which improved fuel–air mixing, shortened combustion duration, thus, resulting in high combustion efficiency and power density. Moreover, with the increase in diameter-to-depth ratio of the B type DLSB, the turbulent kinetic energy and the peak of pressure and heat release rate increased, further increasing power density. Finally, when the DLSB with a diameter-to-depth ratio of 2.0 is coupled with the staggered double-layer arrangement of nozzle holes, the in-cylinder mixtures became more uniform at both the circumferential and radial directions, and the combustion was considerably accelerated, achieving an optimum specific power of 122.6 kW·L−1. Meanwhile, there was a slight decrement for peak pressure and NOx emission, and smoke decreased by 49.1%, which revealed substantial improvement in reduction in mechanical load and emissions.

In order to improve the performance of engines fueled with diesel fuel or diesel-like e-fuels so as to realize greener transportation, the V-type and Y-type intersecting hole nozzles, in which each hole is formed by the coalescence of two or three subholes, have been designed. In this article, the multiphase flow inside and outside the nozzle was numerically investigated using a volume-of-fluid large eddy simulation (VOF-LES) method to clarify the effects of the nozzle structure on the cavitating flow and primary atomization characteristics. The calculation was carried out at an injection pressure of 150 MPa and a back pressure of 0.1 MPa. Numerical results showed that unlike the L-shape pressure distribution along a cylindrical hole, for intersecting type hole nozzles, the pressure showed a stepped shape drop along the holes due to the overall convergent hole structure, which restrained the inception of cavitation. Consequently, the global loss of the flow over an intersecting type hole nozzle was lower by 24–37% than those of a cylindrical hole nozzle. Additionally, the jets emerging from the intersecting hole nozzles showed 50% wider spreading angles and 27% smaller droplet sizes than those of the cylindrical hole nozzle. Furthermore, the jets emerging from a Y-type intersecting hole nozzle showed enhanced atomization, which was found to be due to the unstable air suction near the outlets of this type of nozzle hole.

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.

Multiple-objective optimization of a heavy-duty compression ignition engine fueled by gasoline/hydrogenated catalytic biodiesel (HCB) blends at low loads was performed by employing the KIVA-3V code and genetic algorithm. In addition, the mechanism of multiple-injection and sensitivity of operating parameters on engine performance of the optimal cases were also explored. The results indicated that efficient combustions for G70H30 (70% gasoline and 30% HCB) and G100 (pure gasoline) with ultra-low nitrogen oxides (NOx) and soot emissions could be obtained after optimization. As HCB fraction increases, the ranges of operating parameters become more extensive, and the required initial temperature for optimal cases can be effectively reduced. When the main injection occurs after the ignition caused by pilot injection, main injection moderates the heat release rate (HRR) by creating concentration and temperature stratifications in the spray area simultaneously, and the exhaust gas recirculation (EGR) rate, pilot, and main start of injections and pilot fraction play dominant roles on engine performance. Moreover, when main injection is much more advanced than the ignition timing, main injection controls the HRR only through the concentration stratification in the reaction zone, and the EGR rate, initial temperature, and pilot faction have dominated effects on engine performance.

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.

The emphasis of this paper is to explore the gas-liquid interface characteristics of binary-component n-alkane fuels composed of n-heptane and n-dodecane at sub/supercritical nitrogen environments, and examine the vapor-liquid equilibrium (VLE) assumption adopted in the continuum-based vaporization models using the molecular dynamics simulation. In addition, the phase transition characteristics are also revealed. The results indicate that the vaporization of the binary-component fuel follows the classical multi-component vaporization theory in subcritical environment, in which the preferential vaporization of the light-end component is obvious with distinguishing gas-liquid interface. On the contrary, in supercritical environment, the vaporization rates of light-/heavy-end components are simultaneously enhanced even in the early stage. When approaching the critical point of the heavy-end component, the solubility of the ambient gas of nitrogen in the liquid phase is greatly enhanced with the indistinguishable gas-liquid interface. The transition mechanism from VLE to non-VLE for single-component fuels is caused by the remarkable ambient gas solubility in the liquid phase and the non-ideal gas effect at high pressures. However, for binary-component fuels, it is related to the complicated interaction between the light- and heavy-end components with significant differences in the physical properties and critical points. It is also found that ambient temperature and pressure play more dominant roles in controlling the phase transition process compared to the light-end component blended ratio for the binary-component fuels.

The heat transfer performance of ground heat exchanger is significant to the ground source heat pump. The soil thermal parameters, the groundwater advection and the different borehole field layout are important factors to affect the performance of ground heat exchanger. Therefore, the influence of groundwater advection velocity, soil physical parameters and different borehole field layout on the soil temperature distribution and evolution around the ground heat exchanger has been analyzed and studied with unbalanced seasonal thermal load based on the moving finite line heat source model with groundwater advection. The results show that the heat accumulation is easy to occur as the time develops when the groundwater advection is taken into consideration. No matter what type of geological condition is employed, a reasonable borehole field layout can effectively avoid heat accumulation problems under the condition of keeping the same amount boreholes without changing the original ground area. The borehole field layout dispersed along the center line of the advection and concentrated in the advection downstream relatively can effectively reduce the heat accumulation.

Precise control of needle lift provides one possibility to control the Diesel spray and combustion process actively. However, most studies of needle lift focus on internal flow or near nozzle spray. Little work has been performed on its effects on reacting spray. In this work, one way to change the needle lift profile of a solenoid injector has been developed and the relationship between needle lift and reacting spray has been investigated. The needle movement was detected with an optical nozzle. In addition, the visualization of reacting sprays of the same injector equipped with a single-hole nozzle was conducted in a combustion chamber. Some simulations were also performed to assist the analysis. The results show that the needle lift profile can be regulated by changing the thickness of an adjusting pad. It seems the different needle lift profiles do not bring in significant influences on reacting spray characteristics. The CFD results indicate that it is mainly caused by the similar internal flow characteristics which do not show strong variation when needle lift is higher than 0.1 mm. However, the discharge coefficient and velocity coefficient decrease sharply when needle lift is smaller than 0.05 mm because of the “throttle” effect.

The raw Jojoba oil is utilized to produce biodiesel via a transesterification process, which is optimized using smoke point, yield, and viscosity of produced biodiesel, as well as the final product, is characterized utilizing GC-MS and FTIR. Then, the combustion and emission characteristics of Jojoba oil biodiesel-Jet-A1 blends are performed utilizing a lean premixed pre-vaporized combustion (LPP) approach. The JME with two blending ratios of 10% and 20% by volume and jet fuel of 90% and 80% by volume, as well as the pure jet fuel, are burned in an LPP combustor at two different equivalence ratios of 0.87 and 0.95 to investigate the suitability of using the JME-jet A1 fuel blends as an alternative energy resource. The LPP combustor is designed precisely regarding a comprehensive survey of the main parameters affecting on it, and its combustion results show that it has an acceptable and stable flame. The results indicate that the NOx emission decreases with enlarging the volume fraction of JME, while the CO and UHC formation increase. The flame temperature distributions are similar for the different tested fuels. It can be deduced that Jojoba biodiesel can be used up to 20% by volume as an alternative fuel with jet fuel in a commercial application.

A detailed experimental investigation on the effect of thermal properties on single droplet combustion characteristics has been performed at room temperature and atmospheric pressure under normal g...

In order to treat waste during oleic acid production, pyrolysis method was used to investigate the plant oil asphalt (POA) to obtain bio-fuel. It was found that the compounds contained alkane, alkene, fatty acid, plant sterol derivatives, alcohol and etc. in pyrolysis products of POA by Pyrolysis-Gas Chromatography-Mass Spectrometer (Py-GC-MS). The Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (ESI FT-ICR-MS) results showed that dehydrogenation and polymerization reactions took place during the pyrolysis process, but the main reaction was decarboxylation. According to van Krevelen diagram the nature of the bio-fuel can be evaluated. The acid value and viscosity of the resulting bio-fuel produced were higher than that of diesel fuel and reference bio-fuel. The calorific value showed a slight lower value than that of diesel oil. These studies nominated POA as a potential renewable feedstock for bio-fuel production the simple pyrolysis method.

The main challenge of utilizing ethanol in diesel engines in blending mode is the phase separation issue. Therefore, an attempt has been performed to enhance the stability feature of ethanol/Jatrop...

The cavitating flow in diesel injector nozzles plays a vital role in spray atomization and formation of fuel–air mixture, since vortex-induced string cavitation has recently been found a much more influence on spray compared to the ordinary geometry-induced film cavitation. In this study, in order to investigating string cavitation and its’ enhancement on spray, the visualization experimental platform for the real-size optical tapered-hole nozzle was built based on the high-pressure common rail fuel injection system. Groups of optical nozzles with different geometries were designed for exploring the couple effects of several nozzle geometric parameters, including nozzle sac chamber depth, nozzle-hole position height and needle lift, on the three-dimension vortex flow structure and then on the string cavitation and spray characteristics. Results indicated that the string cavitation characteristics are tightly associated with couple characteristics of the parameters. The stable and strong string cavitation during the whole injection process can be obtained in the Min-sac nozzle with the high hole position under the low needle lift. The string cavitation extends to the nozzle-hole outlet, and subsequently induces the special hollow cone spray with air in the spray center location and corresponding a larger spray cone angle even under not so high injection pressure.

In the current study, the n-heptanol is mixed with methyl oleate biodiesel fuel at different blends which are 10%, 20% and 40% (by volume) n-heptanol+90%, 80%, 60% methyl oleate fuel (H10B, H20B, and H40B) to examine the combustion and exhaust emission characteristics of a rapid compression-expansion machine (RCEM). The RCEM is operated under diesel engine condition with fixed inlet air properties. The findings for methyl oleate show that the peak pressure is slightly reduced, while soot and NOx emissions are reduced by about 60% and 3% respectively compared to pure diesel fuel. Furthermore, the blending of n-heptanol with methyl oleate fuel leads to a considerable reduction in the soot emission by about 75% and the NOx emission is reduced by 6% compared to pure methyl oleate fuel. The flame images confirm that there is a reduction in flame temperatures for methyl oleate compared to pure diesel fuel. Additionally, the combustion process is retarded with increasing the blending ratio of n-heptanol in the fuel mixture. Based on the combustion and emission characteristics, the recommended blending ratio of n-heptanol and methyl oleate fuel is H20B.

This article aims to study the influence of the addition of graphene oxide nanoparticles (GO) to diesel/higher alcohols blends on the combustion, emission, and exergy parameters of a CI engine unde...

In this work, broadband luminosity was used to detect ignition delay and diffused back-illumination extinction imaging was employed to measure soot property with different double-injection strategies in a constant volume combustion chamber under different ambient conditions. The interaction between the two-stage injections have been studied experimentally with two key parameters, dwell time and first injection duration. Results show that in two-stage injection cases, a faster flame propagation speed and a more homogeneous soot concentration distribution were observed in the second injection. Besides, averaged KL value in soot regions of the second injection is slightly less than that of the first one. The first injection has a better effect on the ignition delay of the second injection under low ambient pressure. Meanwhile, the soot onset time of the second injection is advanced more obviously. However, compared with the first injection, the advance amount of the ignition delay and the soot onset time of the second injection shows no particular sensitivity with ambient temperature. With longer pilot injection duration, the initial sooting location of the main injection shows a slight reduction but the total soot mass seems to be constant with the variation of the pilot injection duration.

Catalytic co-pyrolysis of seaweed Enteromorpha clathrata (EN) and cellulose (CEL) with catalysts ZSM-5 and MCM-41 was investigated by TG, Py–GC/MS and fixed-bed experiments. The effects of temperature, catalysts, seaweed and cellulose ratio were examined on product yields distribution and bio-oil compositions by catalytic co-pyrolysis. The maximum bio-oil yield was recorded at the ratio of 1:1 (EN and CEL) with ZSM-5/MCM-41 at 500 °C on co-pyrolytic process. The interaction of radicals and faster heat transfer rate of EN/CEL induces the synergistic effects with catalysts. The advantage of mesoporous molecular sieve along with acidic microporous zeolite of ZSM-5/MCM-41 improved the cracking, dehydration, decarbonylation, decarboxylation, dealkylation, aromatization, oligomerization and deamination reactions. The overall study revealed that the amount of N-containing compounds were decreased and significantly elevated bio-oil production with increased furans and aromatics.

Flow inside the diesel nozzle is crucial to spray, combustion, and emissions. This work aimed to improve the understanding of effects of internal fuel-flow on diesel spray, especially the special string cavitating flow. Optical experiments were employed for characterizing the formation of string cavitation inside the transparent scaled-up tapered diesel orifices. Simultaneously, the corresponding evolution of spray cone angles were obtained. Results show that there were two origins of the string cavitation, which were originated from inlet and outlet of the orifice, respectively. Moreover, there were two typical development processes of the string cavitation between hole and hole, which were defined as type-A and type-B string cavitation. Furthermore, effects of string cavitation were analyzed: it could trigger the geometry-induced cavitation and make a sharp increase of spray cone angle. Finally, the relationships between the occurrence regularity of string cavitation, the needle lift and the injection pressure were revealed by comparison of different needle lifts and different injection pressures.