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Deep reinforcement learning (DRL) is a promising approach to establish energy management strategies (EMSs) for hybrid electric vehicles and how to deal with physical constraints is one of the key challenges in DRL-based EMSs. This paper established a DRL-based EMS for a power-split hybrid electric vehicle and a novel reward function with punishments on irrational actions is proposed based on a rough model of the vehicle. Twin Delayed Deep Deterministic Policy Gradient (TD3), which could enhance the capability of dealing with complicated tasks than the widely-used Deep Deterministic Policy Gradient (DDPG), is adopted to enable online optimization of the EMS. Simulation study with the vehicle model has been conducted to compare the two algorithms using different tasks. In contrast to the DDPG-based EMS, the TD3-based one can obtain the optimal policy with the computation time reduced by 10% and the fuel consumption by 7.28% in complicated tasks including physical constraints recognition and avoiding. Whereas in the simple tasks irrespective of constraints, similar performance has been achieved. It is demonstrated that TD3 is more suitable for complicated tasks and more robust than DDPG.

Significance High concentrations of ultrafine particles (UFPs), approaching 1 million/cm3, are frequently produced from new particle formation under urban environments, but the fundamental mechanisms regulating nucleation and growth for UFPs are poorly understood. From simultaneous ambient and environmental chamber measurements, we demonstrate remarkable formation of UFPs from urban traffic emissions. By replicating ambient conditions using an environmental chamber method, we elucidate the roles of existing particles, photochemistry, and synergy of multipollutant photooxidation in nucleation and growth of UFPs. Our results reveal that synergetic oxidation of vehicular exhaust leads to efficient formation of UFPs under urban conditions. Recognition of this large urban source for UFPs is essential to accurately assessing their impacts and to effectively developing mitigation policies., High levels of ultrafine particles (UFPs; diameter of less than 50 nm) are frequently produced from new particle formation under urban conditions, with profound implications on human health, weather, and climate. However, the fundamental mechanisms of new particle formation remain elusive, and few experimental studies have realistically replicated the relevant atmospheric conditions. Previous experimental studies simulated oxidation of one compound or a mixture of a few compounds, and extrapolation of the laboratory results to chemically complex air was uncertain. Here, we show striking formation of UFPs in urban air from combining ambient and chamber measurements. By capturing the ambient conditions (i.e., temperature, relative humidity, sunlight, and the types and abundances of chemical species), we elucidate the roles of existing particles, photochemistry, and synergy of multipollutants in new particle formation. Aerosol nucleation in urban air is limited by existing particles but negligibly by nitrogen oxides. Photooxidation of vehicular exhaust yields abundant precursors, and organics, rather than sulfuric acid or base species, dominate formation of UFPs under urban conditions. Recognition of this source of UFPs is essential to assessing their impacts and developing mitigation policies. Our results imply that reduction of primary particles or removal of existing particles without simultaneously limiting organics from automobile emissions is ineffective and can even exacerbate this problem.

In the present work, we conducted experiments of secondary organic aerosol (SOA) formation from urban cooking and vehicular sources to characterize the mass spectral features of primary organic aerosol (POA) and SOA using an high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Our results showed that the cooking styles have a greater impact on aged COA (cooking organic aerosol) mass spectra than oxidation conditions. However, the oxidation conditions affect the aged HOA (hydrocarbon-like OA) spectra more significantly than vehicle operating conditions. In our study, we use mass spectra similarity analysis and positive matrix factorization (PMF) analysis to establish the POA and SOA mass spectra of these two sources. These mass spectra are used as source constraints in a multilinear engine (ME-2) model to apportion the OA (organic aerosol) sources in the atmosphere. Compared with the traditional ambient PMF results, the improved ME-2 model can better quantify the contribution of POA and SOA from cooking and vehicular sources. Our work, for the first time, establishes the vehicle and cooking SOA source profiles, and can be further used in the OA source apportionment in the ambient atmosphere.

This study investigated polycyclic aromatic hydrocarbons (PAHs) and soot formation characteristics in laminar jet flames fuelled by primary reference fuels (PRFs) at elevated pressures. Qualitative PAHs and quantitative soot profiles were acquired by using laser-induced fluorescence and laser-induced incandescence, respectively. The backpressure of flames ranged from 1 bar to 5 bar. Proper flames with the volume fraction of iso-octane in PRFs varying between 0% and 100% and flame equivalent ratio varying between 3.0 and 11.4 were stabilised in a pressurised chamber. The effects of backpressure, equivalent ratio and iso-octane ratio on PAHs and soot formation were evaluated. PAHs and soot formation can be promoted by increasing iso-octane ratio, equivalent ratio and backpressure. The data suggest that PAHs with large molecular size are more sensitive to the increase of backpressure compared with those with small molecular size. Backpressure played a positive role in the growth of PAHs size. The averaged soot volume fraction showed an approximate power-law relation with pressure. The measured averaged soot volume fraction was proportional to pn. Pressure exponent n was 1.34–2.17, 1.41–2.12 and 1.56–2.20 at equivalent ratios of 6.2, 8.5 and 11.4, respectively.

In this research, n-hexane flashing jets discharged from two-hole GDI injectors were studied numerically with different superheat levels and inter-hole angles. The mutual interaction between under-expanded flashing jets was discussed in terms of its effect and mechanism. It was found that under certain conditions, the jets deflected towards each other and merged into one jet which moved along the central axis, indicating the occurrence of spray collapse. The spray collapse is ascribed to the pressure drop in the central area between the two jets, which is an effect of the low-pressure cores within individual jets. The pressure drop in the central area is mainly determined by two effects, i.e. the intensity and volume of the low-pressure cores in individual jets, and the formation of the secondary cell which protects the central area from being affected by the ambience. In the transitional stage from non-collapse to fully-collapse, the pressure drop was enhanced with the rise of superheat level or the decrease of inter-hole angle, and the extent of spray collapse increased. Besides, unique shock structures similar to those of under-expanded gaseous twin-jets were formed at high superheat levels, which consist of two primary cells and a secondary cell.

Evaporation processes of a fuel droplet under sub- and supercritical ambient conditions have been studied using molecular dynamics (MD) simulations. Suspended n-dodecane droplets of various initial diameters evaporating into a nitrogen environment are considered. Both ambient pressure and temperature are varied from sub- to supercritical values, crossing the critical condition of the chosen fuel. Temporal variation in the droplet diameter is obtained and the droplet lifetime is recorded. The time at which supercritical transition happens is determined by calculating the temperature and concentration distributions of the system and comparing with the critical mixing point of the n-dodecane/nitrogen binary system. The dependence of evaporation characteristics on ambient conditions and droplet size is quantified. It is found that the droplet lifetime decreases with increasing ambient pressure and/or temperature. Supercritical transition time decreases with increasing ambient pressure and temperature as well. The droplet heat-up time as well as subcritical to supercritical transition time increases linearly with the initial droplet size d0, while the droplet lifetime increases linearly with d 0 2 . A regime diagram is obtained, which indicates the subcritical and supercritical regions as a function of ambient temperature and pressure as well as the initial droplet size.

This paper is to investigate the characteristics of trans-critical propane spray compared with the flash boiling spray ejected from a multi-hole injector in a constant volume chamber by using the Schlieren and backlit imaging methods. The fuel temperature ( T f ) is set from 30 °C to 120 °C, injection pressure ( p f ) from 60 bar to 120 bar and ambient pressure ( p a ) from 0.2 bar to 10 bar. The results show that the trans-critical spray has longer vapor penetration and shorter liquid penetration than the flash boiling spray, but those two sprays have similar curve liquid boundaries near the nozzle. Several discernable collapsed shock structures near the nozzle are observed at T f = 120 °C, p f =120 bar, p a = 1 bar, but they disappear when p f drops to 60 bar for the transition path may not enter the two-phase region, and the liquid phase hardly occurs. The Mach disk distance of trans-critical spray in this study is larger than that of the under-expanded ideal gas jet because of the collapse phenomenon. At T f = 120 °C, p f = 120 bar, the liquid length decreases when p a increases from 0.2 bar to 2.5 bar and increases when p a continues to rise.

In the present work, we conducted experiments of secondary organic aerosol (SOA) formation from urban lifestyle sources (cooking and vehicle) to characterize the mass spectral features of primary organic aerosol (POA) and SOA using an high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Our results showed that the cooking styles have greater impact on aged COA mass spectra than oxidation condition. However, the oxidation conditions affect the aged HOA spectra more significantly than vehicle operation conditions. In our study, we use mass spectra similarity analysis and positive matrix factorization (PMF) analysis to establish the POA and SOA mass spectra of these two typical lifestyle sources. These mass spectra are used as source constraints in a multilinear engine (ME-2) model to apportion the OA sources in the atmosphere. Comparing with the traditional ambient PMF results, the improved ME-2 model can better quantify the contribution of POA and SOA from life-style sources. Our work, for the first time, establishes the vehicle and cooking SOA source profiles, and can be further used in the OA source apportionment in the ambient atmosphere.

Both vehicle exhaust and cooking emission are closely related to the daily life of city dwellers, which are considered as major sources of urban secondary organic aerosol (SOA). Here, we defined the SOA derived from vehicle exhaust and cooking emission as Urban Lifestyle SOA, and simulated their formation using a Gothenburg potential aerosol mass reactor (Go: PAM). After samples had been aged under 0.3–5.5 days of equivalent photochemical age, these two urban lifestyle SOA showed markedly distinct features in SOA mass growth potentials, oxidation pathways and mass spectra. The SOA / POA mass ratios of vehicle groups (107) were 44 times larger than those of cooking groups (2.38) at about 2 days of equivalent photochemical age. It reveals that organics from vehicle may undergo the alcohol/peroxide and carboxylic acid oxidation pathway to produce abundant less/more oxidized oxygenated OA (LO-OOA and MO-OOA), and only a few primary hydrocarbon-like organic aerosol (HOA) remains unaged. In contrast, organics from cooking may undergo the alcohol/peroxide oxidation pathway to produce moderate LO-OOA, and comparable primary cooking organic aerosol (COA) remains unaged. Our findings provide an insight into atmospheric contributions and chemical evolutions for urban lifestyle SOA, which would greatly influence the air quality and health risk assessments in urban areas.

In the present work, we performed chassis dynamometer experiments to investigate the emissions and secondary organic aerosol (SOA) formation potential of intermediate volatility organic compounds (IVOCs) from an on-road Chinese gasoline vehicle. High IVOCs emission factors (EFs) and distinct volatility distribution were recognized. The IVOCs EFs for the China V vehicle ranged from 12.1 to 226.3 mg · kg-fuel−1, with a median value of 83.7 mg · kg-fuel−1, which is higher than that from US vehicles. Besides, large discrepancy in volatility distribution and chemical composition of IVOCs from Chinese gasoline vehicle exhaust is discovered, with larger contributions of B14-B16 compounds and higher percentage of n-alkanes. Further we investigated the possible reasons that influence the IVOCs EFs and volatility distribution and found that fuel type, starting mode, operating cycles and acceleration rates could have an impact on the IVOCs EF. When using E10 (ethanol volume ratio of 10 %, v / v) as fuel, the IVOCs EF of the tested vehicle was lower than that using commercial China standard V fuel. Cold-start operation has higher IVOCs EF than hot-start operation. Chinese Light vehicles Test Cycle (CLTC) produced 70 % higher IVOCs than those from the World-wide harmonized Light-duty Test Cycle (WLTC). We found that vehicle emitted more IVOCs at lower acceleration rates, which leads to high EFs under CLTC. The only factor that may influence the volatility distribution and compound composition is the engine-aftertreatment system, which has compound and volatility selectivity in exhaust purification. These distinct characteristics in EFs and volatility may result in higher SOA formation potential in China. Using published yield data and surrogate equivalent method, we estimated SOA formation under different OA loading and NOx conditions. Results showed that under low and high NOx conditions at different OA loadings, IVOCs contributes more than 80% of the predicted SOA. Furthermore, we built up a parameterization method to simply estimate the vehicular SOA based on our bottom-up measurement of VOCs and IVOCs, which would provide another dimension of information when considering the vehicular contribution to the ambient OA. Our results indicate that vehicular IVOCs contribute significantly to SOA, implying that the importance of reducing IVOCs when making air pollution controlling policies in urban area of China.

Internal combustion (IC) engines operating on fossil fuel oil provide about 25% of the world's power (about 3000 out of 13,000 million tons oil equivalent per year-see Figure 1), and in doing so, they produce about 10% of the world's greenhouse gas (GHG) emissions (Figure 2). Reducing fuel consumption and emissions has been the goal of engine researchers and manufacturers for years, as can be seen in the two decades of ground-breaking peer-reviewed articles published in this International Journal of Engine Research (IJER). Indeed, major advances have been made, making today's IC engine a technological marvel. However, recently, the reputation of IC engines has been dealt a severe blow by emission scandals that threaten the ability of this technology to make significant and further contributions to the reduction of transportation sector emissions. In response, there have been proposals to replace vehicle IC engines with electric-drives with the intended goals of further reducing fuel consumption and emissions, and to decrease vehicle GHG emissions

Fuel saving and emission reduction are big challenges in the development of diesel engines. Diesel particulate filters (DPF) can effectively reduce particulate matter (PM) emissions of diesel engines but negatively affect the engine fuel economy. Some previous studies have been conducted to investigate the effects of DPFs on engine fuel economy, however, nearly all previous studies have neglected the impact of ash accumulation on DPF related fuel penalty. This work aims to quantitatively estimate the impact of ash accumulation on DPF related fuel penalty for a typical modern on-road heavy-duty diesel engine. For this purpose, a one-dimensional full-size DPF model considering ash effects was built and validated in this work, and an engine bench test was conducted to evaluate the effects of exhaust backpressure on engine fuel consumption. An estimation method for the quantitative evaluation of the impact of ash accumulation on DPF related engine fuel penalty was proposed based on the model and experimental data. Subsequently, the impact of ash accumulation on DPF lifetime fuel penalty as well as the potential of fuel saving by DPF ash management for a typical modern on-road heavy-duty diesel engine were quantitatively analyzed. In addition, the effects of engine-out PM emission concentration and DPF maximum soot loading prior to regeneration on the impact of ash accumulation on DPF lifetime fuel penalty and the fuel saving potential of DPF ash management are investigated with the estimation method. The results showed that the DPF ash induced fuel penalty ranged from 0.02% to 0.42% for the typical modern on-road heavy-duty diesel engine studied in this work, and the DPF lifetime fuel penalty could be reduced by optimizing the DPF ash cleaning interval. The fuel saving potential of DPF ash management ranged from 0.22% to 0.69% for all the cases studied in this work, which has the similar magnitude to some specific individual applications such as engine friction reduction, lowering accessory losses, or pumping optimization. Both the DPF ash induced fuel penalty and the fuel saving potential of DPF ash management are increasing with the rise of engine-out PM emission concentration no matter the DPF control strategy is implemented without or with ash correction, while the DPF maximum soot loading prior to regeneration showed little effects on the ash induced fuel penalty and the fuel saving potential of DPF ash management.

Chassis dynamometer experiments were conducted to investigate the effect of vehicle speed and usage of ethanol-blended gasoline (E10) on formation and evolution of gasoline vehicular secondary organic aerosol (SOA) using a Gothenburg Potential Aerosol Mass (Go: PAM) reactor. The SOA forms rapidly, and its concentration exceeds that of primary organic aerosol (POA) at an equivalent photochemical age (EPA) of ~1 day. The particle effective densities grow from 0.62 ± 0.02 g cm−3 to 1.43 ± 0.07 g cm−3 with increased hydroxyl radical (OH) exposure. The maximum SOA production under idling conditions (4259–7394 mg kg-fuel−1) is ~20 times greater than under cruising conditions. There was no statistical difference between SOA formation from pure gasoline and its formation from E10. The slopes in Van Krevelen diagram indicate that the formation pathways of bulk SOA includes the addition of both alcohol/peroxide functional groups and carboxylic acid formation from fragmentation. A closure estimation of SOA based on bottom-up and top-down methods shows that only 16%–38% of the measured SOA can be explained by the oxidation of measured volatile organic compounds (VOCs), suggesting the existence of missing precursors, e.g. unmeasured VOCs and probably semivolatile or intermediate volatile organic compounds (S/IVOCs). Our results suggest that applying parameters obtained from unified driving cycles to model SOA concentrations may lead to large discrepancies between modeled and ambient vehicular SOA. No reduction in vehicular `SOA production is realized by replacing normal gasoline with E10.

Today, the problem of energy shortage and climate change has urgently motivated the development of research engaged in improving the fuel efficiency of internal combustion engines (ICEs). Although many constructive alternatives—including battery electric vehicles (BEVs) and low-carbon fuels such as biofuels or hydrogen—are being put forward, they are starting from a very low base, and still face significant barriers. Nevertheless, 85–90% of transport energy is still expected to come from combustion engines powered by conventional liquid fuels even by 2040. Therefore, intensive passion for the improvement of engine thermal efficiency and decreasing energy loss has driven the development of reliable approaches and modelling to fully understand the underlying mechanisms. In this paper, literature surveys are presented that investigate the relative advantages of technologies mainly focused on minimizing energy loss in engine assemblies, including pistons and rings, bearings and valves, water and oil pumps, and cooling systems. Implementations of energy loss reduction concepts in advanced engines are also evaluated against expectations of meeting greenhouse gas (GHG) emissions compliance in the years to come.

As the key components that provide path for reactant and water transportation, the impact of gas diffusion layer (GDL) and micro-porous layer (MPL) on the performance of proton exchange membrane fuel cells (PEMFCs) has been extensively investigated. However, as a non-uniform porous medium, the study considering real spatially variable properties of GDL and MPL is really insufficient. In order to investigate the role of MPL with real spatially variable properties on PEMFCs performance and water management, a three-dimensional multi-phase model, which couples the catalyst layer agglomerate sub-model, is developed. It is found the uniform medium assumption for GDL and MPL might overstate the fuel cells performance when the output voltage is higher than 0.5V, especially under the high inlet relative humidity (RH). Besides, the spatially variable properties cause non-uniform distribution of liquid water and there are some saturation peaks in the middle or sides of GDL. Finally, the impact of inlet RH under different types of GDL and MPL is also discussed. From the perspective of the real spatially variable properties of GDL and MPL, this research provides a new approach to explore the influence mechanism of MPL.

HONO plays a key role in atmospheric chemistry, and while its importance is well-known, the sources of HONO are still not completely understood. As a component of ambient HONO sources, direct emission from vehicles is an area that should be extensively studied. In this study, we determined the HONO emission index for typical gasoline vehicles in the car population of China through a chassis dynamometer with different types of engines (PFI/GDI), starting conditions (cold/warm) and running styles (Beijing cycle). Emission ratios of HONO to nitrogen oxide (NO X ) for the Chinese gasoline cars are determined to be in the range of (0.03–0.42) % and an averaged value is about 0.18%, which are comparable to those reported in the few studies available in Europe, the United States and Japan for gasoline cars while smaller for those of the diesel cars. The atmospheric impact of the direct HONO emission from gasoline cars was analyzed for a typical urban site in Beijing, significant contributions of the direct emission toward the HONO budget were found during morning rush hours or twilight conditions to be 8–12%.

Emissions from gasoline vehicles have recently become one of the main causes for urban air pollution. In this work, individual particles of particulate matter emitted from the gasoline engines on the test bench were characterised using transmission electron microscopy coupled with energy-dispersive X-ray spectrometry (TEM-EDX). Effects of the engine types (gasoline direct injection (GDI) engines and port fuel injection (PFI) engines), fuel components (F1–5), engine loads (25, 50, and 75%), and three-way catalyst (TWC) on particulate emissions were tested. The results show that there were six types of individual particles emitted from gasoline engines including soot, organic particles, Fe-rich particles, S-rich particles, Mn-rich particles, and Ca-rich particles, in which the organic, soot, and S-rich particles were predominant types. The particles emitted from GDI engines had a higher percentage of soot and lower percentage of organic particles compared to those from PFI engines. Fuel types also influenced compositions of the emitted particles. F1 produced a relatively high percentage of organic particles. Compared to F1, F2 containing more aromatics contributed a higher percentage of soot particles; F3 containing MMT (methylcyclopentadienyl manganese tricarbonyl) led to a considerably higher percentage of soot particles, and F4 gasoline (addition of 10% ethanol by volume) produced a lower percentage of soot particles. Compared to F1, F5 with a lower olefin content produced a lower percentage of organic particles. In addition, with increasing load, the relative percentages of soot increased, while the relative percentages of organic particles decreased. Finally, when TWC was used, the percentage of soot increased significantly in association with an increase in particle sizes.

Diesel and Polyoxymethylene Dimethyl Ethers (PODE 3 – 4 )/diesel blends with 10–30% PODE 3 – 4 by volume were tested in a light-duty (LD) direct injection diesel engine without any modifications on the engine fuel supply system. Engine performance, combustion and emission characteristics were compared at various loads. The results show that diesel engines are able to work normally fueled by blend fuel ratio with lower than 30% PODE 3 – 4 . Adding PODE 3 – 4 improve engine efficiency and reduce soot and CO emissions significantly without a serious impact on NOx emissions. P20 is the optimal choice among these blends because it has much lower soot emissions than diesel and P10 and slightly lower NOx emissions than P30. The European Stationary Cycle (ESC) was also carried out in a six-cylinder heavy-duty (HD) production diesel engine fueled with pure diesel and P20, and the results were similar to those of the LD engine. It is proved that PODE 3 – 4 , of which the mass production has been achieved recently, is a promising additive component for diesel fuel.

High fluctuation in cyclic variations influences engine combustion negatively, leading to higher fuel consumption, lower performance, and drivability problems. This paper examines the impacts of injection strategies (injection pressure, injection timing and injection duration) on the cyclic variation of gasoline spark ignition (SI) optical engine under clean and fouled injectors. The principal oscillatory modes of the cycle to cycle variation have been identified, and the engine cycles over which these modes may persist are described. Through the wavelet power spectrum, the presence of short, intermediate and long-term periodicities in the pressure signal have been detected. It was noticed that depending on the clean and fouled injector, the long and intermediate-term periodicities may span many cycles, whereas the short-period oscillations tend to appear intermittently. Information of these periodicities could be helpful to promote efficient control strategies for better combustion. The outcomes report that the cyclic variation of the IMEP happens on multiple timescales, and thus, display complex dynamics. As the fouled injector used, mainly intermittent high-frequency fluctuations are recognized.

Air pollution is particularly severe in developing megacities, such as Beijing, where pollutants from vehicles equipped with modern gasoline direct injection (GDI) engines must be paid enough attention. This study presents the characteristics of individual particles emitted by a GDI gasoline vehicle and their ageing in a smog chamber under the Beijing urban environment, as part of the Atmospheric Pollution & Human Health (APHH) research programme. Using electron microscopy, we identified the particles emitted from a commercial GDI-engine vehicle running under various conditions, namely cold start, hot start, hot stabilized running, idle, and acceleration states. Our results show that most of the particles were organic, soot and Ca-rich ones, with small quantities of S-rich and metal-containing particles. In terms of grain size, the particles exhibited a bimodal distribution in number vs size, with one mode at 800–900 nm, and the other at 140–240 nm. The amounts of organic particles emitted under hot start and hot stabilized states were higher than those emitted under other conditions. The amount of soot particles was higher under cold start and acceleration states. Under the idle state, the proportion of Ca-rich particles was highest, although their absolute number was low. In addition to quantifying the types of particles emitted by the engine, we studied the ageing of the particles during 3.5 hours of photochemical oxidation in an environmental chamber under the Beijing urban environment. Ageing transformed soot particles into core-shell structures, coated by secondary organic species, while the content of sulfur in Ca-rich and organic particles increased. Overall, the majority of particles from GDI-engine vehicles are organic and soot particles with submicron or nanometric size. The particles are highly reactive; they react in the atmosphere and change their morphology and composition within hours via catalyzed acidification that involves gaseous pollutants under high pollution levels in Beijing.

Water management, particularly in the gas diffusion layers (GDL), plays an important role in the performance and reliability of the proton exchange membrane fuel cells (PEMFCs). In this study, a two-phase multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) is employed to simulate water transport in a reconstructed GDL and the effect of perforation shapes is investigated. The revised pseudopotential multiphase model is adopted to realize high-density ratio, good thermodynamic consistency, adjustable surface tension and high contact angle. The transport characteristics are analyzed in both vertical and horizontal transport directions. The LBM simulation provides detailed results in mesoscale and indicates that the surface tension dominates the process of water transport in the perforated GDL, which exhibits unexpectedly similarities in the vertical and horizontal transport. Besides, it is found that the cone-like perforations perform better than cylinder-like perforations as little water clusters together in the bottom of the perforation. Finally, the optimized perforation with defined parameters is derived and discussed, providing guidelines for improving the GDL performance in engineering applications.

For a multi-component hydrocarbon mixture under supercritical conditions, the mechanism and criterion for the transition of the dominant mixing mode from evaporation to diffusion are not well established. In this paper, phase transition processes of three-component hydrocarbon fuel (5.3 wt% isooctane, 25.8 wt% n-dodecane and 68.9 wt% n-hexadecane) droplets in sub- and supercritical nitrogen environments were studied using molecular dynamics, in comparison with those of single-component n-hexadecane droplets. The initial diameters of the droplets were 25.5 nm (three-component) and 26.5 nm (single-component), respectively. Based on the quantitative Voronoi tessellation, a new criterion, which was a combination of two dimensionless critical values of Hc = 0.85 and Wc = 0.35, was proposed to determine the transition of the dominant mixing mode from evaporation to diffusion during fuel-ambient gas mixing. Results indicated that when the ambient pressure ranged from 2 MPa to 10 MPa and the ambient temperature ranged from 750 K to 1200 K, the density difference between the vapor phase and the liquid phase decreased gradually with increasing ambient pressure or decreasing ambient temperature. And the dominant mixing mode gradually transitioned from evaporation to diffusion. Increasing the ambient pressure did not necessarily promote the occurrence of phase transition, while increasing ambient temperature accelerated the phase transition monotonically. Light fuel components increased the minimum pressure of the diffusive mixing zone. A major finding was that under a certain ambient pressure, the supercritical transition temperature had not only a minimum but also a maximum.

A LNT (lean NOx trap) model coupled with EGR (exhaust gas recirculation) was developed based on the Langmuir–Hinshelwood mechanism to investigate the EGR effects on NOx adsorption pathway of LNT catalysts with temperature changed in range 150℃~550℃. Both the nitrate and nitrite adsorption paths were considered for the NOx storage process in the model as well as the spillover of stored NOx between Ba and Pt sites. The data and validation for modelling were from literatures of predecessors and our previous lean-burn gasoline engine experiment*. The model quantified the contributions of both nitrate route and nitrite route to the NOx storage with change of EGR rate (0%~30%) under raw emission atmosphere from tested gasoline engine. The model captured key feature of different trends of nitrate route and nitrite route with increasing temperature (150℃~550℃) under EGR rate varying from 0% to 25%. The LNT model provided insight of reaction mechanism for interpreting the behaviour of NOx storage with change of GER rate and temperature, which contributed to improve the NOx storage capacity when mapping EGR rate for lean-burn engine and catalyst operation strategy optimization.

Oxygenated fuel components such as the alcohols of 1-butanol and ethanol are well-known for their potential to improve engine combustion and PM emissions, and these particular fuels are receiving ever greater attention due to their renewable nature giving them great CO 2 emission reduction potential. This paper investigates the effect of compression ratio and fuel properties on combustion, gaseous emissions and PM emissions of an experimental single-cylinder direct injection spark ignition (DISI) engine. The tests were carried out at an engine load of 8.5 bar, at various compression ratios between 10.7 and 11.5, with Bu20 (20%vol 1-butanol in gasoline) and E20 (20%vol ethanol in gasoline) fuel blends along with a reference fuel of gasoline. The results show that 1-butanol and ethanol addition to gasoline is effective to advance the MFB50 point and shorten the combustion duration. 1-butanol addition to gasoline is effective to reduce PM number emissions, while NO x reduction is the main benefit of ethanol addition. It is concluded that synergies between compression ratio and alcohol addition to gasoline enable to simultaneously control gaseous and particulate matter emissions while improving fuel economy with respect to standard gasoline combustion.

In this study, soot formation in a Gasoline Direct Injection (GDI) engine is simulated using a Stochastic Reactor Model (SRM Engine Suite) which contains a detailed population balance soot model capable of describing particle morphology and chemical composition. In order to describe the soot formation originating from the wall film, the SRM Engine Suite is extended to include spray impingement and wall film evaporation models. The cylinder is divided into a wall and a bulk zone to resolve the equivalence ratio and temperature distributions of the mixture near the wall. The combustion chamber wall is assumed to exchange heat directly only with the wall zone. The turbulent mixing within each zone and between the two zones are simulated with different mixing models. The effects of key parameters on the temperature and equivalence ratio in the two zones are investigated. The mixing rate between the wall and bulk zone has a significant effect on the wall zone, whilst the mixing rate in the wall zone only has a negligible impact on the temperature and equivalence ratio below a certain threshold. Experimental data are obtained from a four-cylinder, gasoline-fuelled direct injection spark ignition engine operated stoichiometrically. An injection timing sweep, ranging from 120 CAD BTDC to 330 CAD BTDC, is conducted in order to investigate the effect of spray impingement on soot formation. The earliest injection case (330 CAD BTDC), which produces significantly higher levels of particle emissions than any other case, is simulated by the current model. It is found that the in-cylinder pressure and the heat release rate match well with the experimental data. The particle size distribution in the simulation has the same order of magnitude as the experimental one. By tracing the particles in an equivalence ratio-temperature diagram, it is demonstrated that the rich mixture near the wall becomes the source of the soot formation as a result of the wall film evaporation.

Exhaust gas recirculation (EGR) is a well known technique for suppressing knock and reducing nitrous oxide (NOx) emissions in spark-ignition engines, and this technique is now receiving more attention because of the negative effect of EGR on engine particulate emissions. This paper investigates the effect of EGR on engine combustion (in-cylinder pressure and temperature, mass fraction burned (MFB), knock limited maximum brake torque (KLMBT) spark timing, net indicated specific fuel consumption (ISFCnet), exhaust gas temperature) and emissions (NOx, unburned hydrocarbon (HC), particulate matter (PM)) in a direct injection spark ignition (DISI) engine. The tests were carried out in a single-cylinder DISI research engine with engine loads between 5.5 and 8.5 bar indicated mean effective pressure (IMEP) and various EGR ratios of up to 13%. The results show that by adding 12% EGR, the KLMBT spark timing could be advanced by 8 crank angle degrees (CAD) which resulted in a 4.1% fuel consumption reduction at 7.0 bar IMEP. EGR addition generally increased the accumulation mode particles and reduced the nucleation mode particles.

This paper studies the combustion and emission characteristics of three low octane fuels: naphtha, the blend of gasoline and diesel (G70D30), and the blend of gasoline and n-heptane (G70H30) in Multiple Premixed Compression Ignition (MPCI) mode. A commercial diesel fuel is also tested in conventional diesel combustion mode and double injection mode as a comparison. The study is carried out in a single cylinder diesel engine with a compression ratio of 16.7. By varying the common rail pressure, the effect of injection pressure on combustion and emissions is investigated. The results illustrate that the combustion delay of the gasoline-type fuels is extended with the increase of injection pressure. The soot emission decreases at high injection pressure with a penalty of higher CO and HC emissions. Increasing the injection pressure also reduces the particle number in accumulation mode, but produces more in nucleation mode. Among the test fuels, naphtha has the lowest NOx emission due to low combustion temperature but the highest CO and HC emissions. There is no significant difference in particle size distribution for the three fuels. The indicated thermal efficiency of gasoline-type fuels increases with the rise of injection pressure and is higher than that of diesel at high injection pressure. Naphtha has the highest efficiency as a result of its low heat transfer and exhaust loss. The diesel fuel has lower CO and HC emissions than the gasoline-type fuels do, but much higher pressure rise rate, NOx and soot emissions due to high combustion temperature and poor premixing. Therefore, the low octane gasoline fuels are more suitable than the diesel for compression ignition engines in terms of the emissions.

This paper investigates a model-free supervisory control methodology with double Q-learning for the hybrid vehicle in charge-sustaining scenarios. It aims to improve the vehicle’s energy efficiency continuously while maintaining the battery’s state-of-charge in real-world driving. Two new heuristic action execution policies, the max-value-based policy and the random policy, are proposed for the double Q-learning method to reduce overestimation of the merit-function values for each action in power-split control of the vehicle. Experimental studies based on software-in-the-loop (offline learning) and hardware-in-the-loop (online learning) platforms are carried out to explore the potential of energy-saving in four driving cycles defined with real-world vehicle operations. The results from 35 rounds of offline undisturbed learning show that the heuristic action execution policies can improve the learning performance of conventional double Q-learning by achieving at least 1.09% higher energy efficiency. The proposed methods achieve similar results obtained by dynamic programming, but they have the capability of real-time online application. Double Q-learnings are shown more robust to turbulence during the disturbed learning: they realise at least three times improvement in energy efficiency compared to the standard Q-learning. Random execution policy achieves 1.18% higher energy efficiency than the max-value-based policy for the same driving condition. Significant tests show that deciding factor in the random execution policy has little impact on learning performance. By implementing the control strategies for online learning, the proposed model-free control method can save energy by more than 4.55% in the predefined real-world driving conditions compared to the method using standard Q-learning.

Gasoline direct injection (GDI) engine development is facing the great challenges in both fuel economy and particulate emissions. Trade-off is often required in GDI engines to sacrifice fuel economy in order to meet the strict emission regulations. GDI injector deposits have been identified as a potential cause of increased particulate emissions. In this work, a series of experimental tests was conducted on a 1.5 L turbocharged GDI engine to further understand the effect of injector deposits. The deposits formed on the injector tip surface were removed after the 55-hour fouling test and their effects on fuel consumption, in-cylinder combustion, thermal efficiency and engine out emissions were investigated before and after the removal. The spray characteristics of an identical injector under clean and fouled conditions were examined and the deposits inside the injector nozzle holes were observed by a scanning electron microscope. The test injectors were mildly fouled with an average of 1.5% flow rate loss and 1.84% injection pulse width increase. After removing the injector tip surface deposits, the engine combustion phase became advanced and the peak in-cylinder pressure increased. The combustion efficiency was close to 98% and showed no significant change. Although the indicated thermal efficiency was only slightly improved by 0.31–0.44% after removing the tip surface deposits, the particulate emissions were significantly affected and reduced by up to around 45%. At the meantime, NOx emissions moderately increased by approximately 12% after removal and no significant change occurred in the THC and CO emissions.

For gasoline direct injection (GDI) engines, as the exhaust gas temperature decreases, the hydrocarbon-to-particle conversion may occur, generating nucleation mode particles. A three-way catalyst converter (TWC) may have effects on the particle evolution as exhaust temperature decreases. In the present study, the effects of TWCs on particulate matter emissions and hydrocarbon-to-particle conversion process under different exhaust gas temperatures are researched. The particle size distributions are compared between the pre-TWC (upstream of the TWC) and post-TWC (downstream of the TWC) positions. Results show that the reduction of total particle number concentrations is 40–80% after exhaust gas passes the TWC, which is higher at higher load. The TWC has higher reduction efficiencies for particles in smaller size ranges. In the size range of 4–8 nm, the reduction efficiencies for particles are more than 96%. For particles larger than 50 nm, the TWC doesn’t show remarkable effects on particle number (PN) concentrations. The particle evolution and the hydrocarbon-to-particle conversion with regard to the exhaust gas temperatures are also investigated. At the post-TWC position, the PN concentrations of nucleation mode are much lower compared with those of accumulation mode, and not sensitive to exhaust temperature variations. The PN concentrations of nucleation mode at the pre-TWC position with the sampling temperature of 170 °C are slightly higher than those at the post-TWC position. PN concentrations of nucleation mode at the pre-TWC position increase sharply when the sampling temperature decreases from 110 °C to 50 °C. It is suggested that TWCs don’t convert the nucleation mode particles directly, but remove those semi-volatile hydrocarbon components as precursors of nucleation mode particles forming in low exhaust temperatures.

This paper reports the experimental and numerical results of soot formation in laminar coflow diffusion flames of vaporized gasoline/ethanol blends at atmospheric pressure to gain improved understanding of ethanol addition to gasoline on soot formation. Four gasoline/ethanol blends of different ethanol mole fractions in the fuel stream ranging from 0% up to 85%, E0, E20, E50, and E85, were investigated to quantify how soot loading varies with the amount of ethanol blending in the fuel. The laminar coflow diffusion flames were generated using a burner system designed for vaporized liquid fuels. The fuel stream was heavily diluted with nitrogen to lower the boiling points and to prevent the flames from smoking. The soot volume fraction distributions were measured using a 2D line-of-sight attenuation technique. These flames were also modeled numerically using the extensively validated CoFlame code and a recently developed reaction mechanism for gasoline surrogates including PAH formation. The results of experiment and numerical modeling agree quite well in terms of the levels of soot volume fraction and they both show a decrease in the soot loading as more ethanol is added in the fuel stream. The measured peak soot volume fraction occurs in the flame centerline region. The soot model used in this study is unable to capture this experimental feature and predicts the peak soot volume fraction in the co-annular region. Ethanol addition reduces the soot loading primarily by lowering soot inception and PAH condensation rates through decreasing the concentrations of aromatics. Additional measurements in gasoline surrogate/ethanol blend flames indicate that the gasoline surrogate model emulates well the sooting propensity of the real gasoline fuel.

A study to extend the low load limit of the mixture of commercial gasoline and diesel in the compression mode is performed on a single cylinder diesel engine. The additional measures, like intake heating, rebreathing, negative valve overlap, are not employed. By adopting boosting, sweeping the injection pressure and varying the fuel octane number, the minimum fuelling rate and the minimum IMEP gained is compared. Besides, the thermal efficiency and emission results at these operation points are also discussed. The results illustrate that the high intake pressure, the low injection pressure and the low fuel octane number are very effective to extend low load limit. With these strategies, gasoline-type fuels can get the lowest load 0.07 MPa IMEP (0.14 MPa intake pressure and 20 MPa injection pressure) and successfully replace diesel at low load operation points in the compression mode. Increasing the intake pressure and reducing the injection pressure can significantly reduce the minimum fuelling rate and then the minimum IMEP. The minimum IMEP (0.34 MPa) of the calibration point on the original engine at test speed (1600 rpm) can be achieved by G80 without boosting. The combustion efficiency is influenced by the intake pressure and the injection pressure, however, the ISFC is more dependent on the engine load rather than other factors. If there is more over-lean mixture in cylinder when adjusting the experimental conditions, CO and HC emissions are higher. To satisfy the Euro VI regulation on NOx (

Polyoxymethylene dimethyl ethers (PODEn) have high oxygen content, cetane number and solubility in diesel fuel. In this work, pure diesel and PODE 3-4 /diesel blends with 10-20% PODE 3-4 by volume were tested in a light-duty (LD)direct injection diesel engine without any modifications on the engine fuel supply system. Engine performance, combustion and emission characteristics were compared at various loads. The results show that PODE 3-4 /diesel blends improve engine efficiency and reduce engine-out emissions significantly, especially soot emissions. The ESC test cycle in a six-cylinder heavy-duty (HD) production diesel engine fuelled with pure diesel and 20% PODE 3-4 was also conducted and similar results were achieved. It is proved that PODE 3-4 , of which the mass production has been achieved recently, is a promising blending component for diesel fuel.

An advanced combustion strategy namely “multiple premixed compression ignition” (MPCI) can exploit multiple combustion regimes. In this paper, the two-stage premixed combustion (i.e. low-temperature combustion and high-temperature combustion) using relatively low-reactivity and high volatility fuel is uncovered in MPCI mode. The mixture formation and combustion processes of low-octane gasoline MPCI mode is resolved by KIVA–CHEMKIN. The low-octane gasoline (G70H30) modeled in this study is a mixture of 70% gasoline and 30% n-heptane by volume, and it is represented by iso-octane and n-heptane oxidation mechanism. A discrete multi-component (DMC) vaporization model is used to simulate the evaporation process of G70H30, while a simplified 12-step GRI-Mech model and a two-step soot model are applied for the NOx and soot calculation, respectively. As a comparative study, partially premixed compression ignition (PPCI) mode of G70H30 is also simulated using the same numerical models. From the longitudinal and transverse sections of the combustion chamber, temporally and spatially distributed combustion events are found in the MPCI mode. That is to say, the first low temperature premixed compression ignition occurs outside of the piston bowl, and it occurs mainly in the squeeze zone above the piston triggered by the local fuel rich region. Then the second high temperature premixed combustion, which is controlled by the local turbulence resulting from the second fuel injection and chamber wall interaction, is located in the center of the combustion chamber. The temporally and spatially distributed combustion in MPCI mode decreases the local temperature, resulting in less NOx formation and lower heat transfer losses. However, there is no marked combustion distribution phenomenon in the G70H30 PPCI mode, and more NOx is generated due to higher local temperature. In addition, the early first injection of MPCI and PPCI causes spray-liner impingement, and becomes the main source of soot formation in the subsequent combustion processes.

Gasoline vehicles greatly contribute importantly to urban particulate matter (PM) pollution. Gasoline direct injection (GDI) engines, known as their higher fuel efficiency than that of port fuel injection (PFI) engines, have been increasingly employed in new gasoline vehicles. However, the impact of this trend on air quality is still poorly understood. Here, we investigated both primary emissions and secondary organic aerosol (SOA) formation from GDI and PFI vehicles under urban-like condition, using combined approaches involving chassis dynamometer measurement and environmental chamber simulation. The PFI vehicle emits slightly more volatile organic compounds, e.g., benzene and toluene, whereas the GDI vehicle emits more particulate components, e.g., the total PM, elemental carbon, primary organic aerosols and polycyclic aromatic hydrocarbons. Strikingly, a much higher SOA production (by a factor of approximately 2.7) is found from the exhaust of the GDI vehicle than that of the PFI vehicle under the same conditions. More importantly, the higher SOA production found in the GDI vehicle exhaust occurs concurrently with lower concentrations of traditional SOA precursors, e.g., benzene and toluene, indicating a greater contribution of intermediate volatility organic compounds and semivolatile organic compounds in the GDI vehicle exhaust to the SOA formation. Our results highlight the considerable potential contribution of GDI vehicles to urban air pollution in the future.