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In the current global scenario, it is essential to find more effective and practical solutions to mitigate the problem of particulate emissions from vehicles. In this research, particulate emission characteristics with changing GDI pressure or applying a split GDI strategy with different second injection timings were initially explored in a Dual-Fuel Spark Ignition (DFSI) engine, which employs Ethanol Port Injection (EPI) plus Gasoline Direct Injection (GDI). The experimental results show that by increasing GDI pressure ( P G D I ) from 5.5 MPa to 18 MPa, ignition delay ( θ F ) shows a small decrease of 0.68 degrees. The parameters, such as maximum in-cylinder temperature ( T M I ) and exhaust gas temperature ( T E G ), each increase by 53.75 K and 13.84 K. An apparent reduction of 59.5% and 36.26% was achieved for the concentrations of particulate number ( N P ) and particulate mass ( M P ), respectively. Particulate emissions are effectively reduced by a split GDI strategy with an appropriate range of second injection timing ( t G D I 2 ). Under t G D I 2 = −260 °CA, N P and M P concentrations exhibit a relatively lower level. However, by delaying t G D I 2 from −260 °CA to −140 °CA, there is an increase of more than 60% in N P concentration. The research findings help offer new and valuable insights into optimising particulate number and mass emissions from DFSI engines. Moreover, the findings could contribute novel and valuable insights into the optimisation of particulate emission characteristics in DFSI engines. [ABSTRACT FROM AUTHOR]

Cold start in gasoline direct injection engines (GDI) is a critical issue that significantly impacts fuel consumption and emissions. Therefore, it is essential to investigate and improve the spray and air-fuel mixing processes during cold starts. This study employed a complimentary set of optical diagnostic techniques, including line-of-sight(extinction, Schlieren, and long-distance microscopy) and 3D computed tomography (CT), to characterize and understand the cold-start spray dynamics under various fuel temperature and injection pressure conditions. The experiments were conducted in a constant volume spray vessel and the fuel temperature was varied using a coolant circulator, with temperatures reaching as low as -7 °C to simulate cold-start conditions. The cold fuel exhibited longer liquid/vapor penetration lengths compared to hot fuel under low injection pressure conditions. This deterioration in spray characteristics was attributed to the attenuated fuel evaporation and reduced entrainment of ambient air. The 3D spray visualization obtained through the CT algorithm, particularly the cut plane images, revealed that plumes with low fuel temperatures had narrower individual plume widths, resulting in minimized plume-to-plume interaction. Microscopic imaging further confirmed this observation which showed separate plumes in the near-nozzle region for cold fuel conditions. Meanwhile, hot fuel under high injection pressure conditions exhibited complete plume collapsing, leading to a significant amount of liquid fuel remaining in the spray core. The liquid penetration reached 70 mm during the injection period, potentially can cause wall wetting on the piston top or cylinder wall. Based on the experimental findings, this study suggests the application of multiple injections with a moderate level of injection pressure for optimized engine performance and reduced emissions during cold starts.

Methanol and ethanol are considered as potential candidates for alternative fuels in spark-ignited engines and flex-fuel vehicles. Alcoholic fuels have higher latent heat of vaporization ( h f g ), lower boiling-point temperature and higher-octane numbers help the engine run under higher compression ratios, resulting in better efficiency and fuel economy. A numerical study is carried out to understand the spray-breakup and vaporization characteristics of binary blended fuel and ternary fuel blend compared to single-component fuel for gasoline direct injection (GDI) system. Multiple simulations were carried out by substituting individual fuel properties of isooctane with those of ethanol to understand the relative importance and effect of fuel properties on spray characteristics. The spray characteristics of pure isooctane fuel and their blends with ethanol and methanol are studied and compared, and the charge cooling effects for alcoholic fuels have been observed. The Spray G operating condition has been taken from the Engine Combustion Network (ECN) for this study. The simulated data for isooctane has been validated with the experimental data from the ECN, and a similar model setup has been used for pure and blended fuel sprays. The discrete-phase modeling (DPM) approach is carried out, and the Unsteady Reynolds-Averaged Navier–Stokes (URANS) RNG (Renormalization) k-ε turbulence model is considered in understanding the spray characterization. The blended methanol fuels have higher penetration lengths compared with ethanol ones. The penetration of the blended fuels (binary and ternary) is slightly lower than the isooctane. The ternary blends showed spray characteristics similar to those of E85, and it indicates that the ternary blended fuel has the potential to be used as a drop-in fuel for a GDI-based flex-fuel vehicle. [ABSTRACT FROM AUTHOR]

Recent efforts of both researchers and regulators regarding particulate emissions have focused on the contribution and presence of sub-23 nm particulates. Despite being previously excluded from emissions legislation with the particle measurement programme (PMP), the latest regulatory proposals suggest lowering the cut-off sizes for counting efficiencies and the use of catalytic strippers to include solid particles in this size range. This work investigated particulate emissions of a 1.0 L gasoline direct injection (GDI) engine using a differential mobility spectrometer (DMS) in combination with a catalytic stripper. Direct comparison of measurements taken with and without the catalytic stripper reveals that the catalytic stripper noticeably reduced variability in sub-23 nm particle concentration measurements. A significant portion of particles in this size regime remained (58–92%), suggesting a non-volatile nature for these particles. Digital filtering functions for imposing defined counting efficiencies were assessed with datasets acquired with the catalytic stripper; i.e., particle size distributions (PSDs) with removed volatiles. An updated filtering function for counting efficiency thresholds of d65 = 10 nm and d90 = 15 nm showed an increase in particulate numbers between 1.5% and up to 11.2%, compared to the closest previous digital filtering function. However, this increase is highly dependent on the underlying PSD. For a matrix of operating conditions (1250 to 2250 rpm and fast-idle to 40 Nm brake torque), the highest emissions occurred at fast-idle 1250 rpm with 1.93 × 108 #/cm3 using the updated filtering function and catalytic stripper. This setup showed an increase in particulate number of +27% to +390% over the test matrix when compared to DMS measurements without the catalytic stripper and applied counting efficiency thresholds of d50 = 23 nm and d90 = 41.

Recent efforts of both researchers and regulators regarding particulate emissions have focused on the contribution and presence of sub-23 nm particulates. Despite being previously excluded from emissions legislation with the particle measurement programme (PMP), the latest regulatory proposals suggest lowering the cut-off sizes for counting efficiencies and the use of catalytic strippers to include solid particles in this size range. This work investigated particulate emissions of a 1.0 L gasoline direct injection (GDI) engine using a differential mobility spectrometer (DMS) in combination with a catalytic stripper. Direct comparison of measurements taken with and without the catalytic stripper reveals that the catalytic stripper noticeably reduced variability in sub-23 nm particle concentration measurements. A significant portion of particles in this size regime remained (58–92%), suggesting a non-volatile nature for these particles. Digital filtering functions for imposing defined counting efficiencies were assessed with datasets acquired with the catalytic stripper; i.e., particle size distributions (PSDs) with removed volatiles. An updated filtering function for counting efficiency thresholds of d65 = 10 nm and d90 = 15 nm showed an increase in particulate numbers between 1.5% and up to 11.2%, compared to the closest previous digital filtering function. However, this increase is highly dependent on the underlying PSD. For a matrix of operating conditions (1250 to 2250 rpm and fast-idle to 40 Nm brake torque), the highest emissions occurred at fast-idle 1250 rpm with 1 . 93   ×   10 8   # / cm 3 using the updated filtering function and catalytic stripper. This setup showed an increase in particulate number of +27% to +390% over the test matrix when compared to DMS measurements without the catalytic stripper and applied counting efficiency thresholds of d50 = 23 nm and d90 = 41. [ABSTRACT FROM AUTHOR]

Both the EU and China are evaluating the feasibility of lowering the detection limit of particle number (PN) measurement to 10 nm in future legislations, making it necessary to better understand the sub-23 nm particle emission characteristics from state-of-the-art vehicles. In this study, solid PN emissions with a diameter larger than 10 nm and 23 nm (known as SPN10 and SPN23) were compared over the WLTC, RTS95, and a so-called "worst-case" real driving emission (RDE) cycle (highly dynamic/0 °C) using two certification-level particle number counters (PNCs) employing evaporation tube (ET) and catalytic stripper (CS) as volatile particle remover (VPR). The results show that SPN10 emissions were 31.7%, 27.8%, and 15.2% higher than SPN23 over the WLTC, RTS95, and laboratory RDE cycles. Sub-23 nm particles were almost not identified within the engine cold-start phase and tended to be a hot-running pollutant favored by aggressive driving styles (frequent accelerations and high engine loads), fuel-cut during decelerations, and long idles. Lower testing temperature delayed the light-off of catalyst and, therefore, significantly reduced the formation of sub-23 nm particles within the engine warm-up stage. Lowering the detection limit to 10 nm is deemed to provide more public health protection since it will guide manufacturers to pay more attention to vehicle hot-running emissions. [ABSTRACT FROM AUTHOR]

This study focused on the spray development process via spray visualization experiment using different nozzle shape. Specifically, the spray penetration and initial spray angle were determined by high-speed camera and Long distance microscope (LDM) visualization system. Additionally, a sheet beam Nd-YAG laser was used to obtain the spray pattern. The experimental results showed that an injector with a step hole of smaller diameter has a narrower spray angle at the initial injection stage and longer spray penetration compared to an injector with a step hole of larger diameter. In addition, spray penetration was greater for a shorter spray hole length. These results demonstrate that the structure of the step and spray hole for a multi-hole Gasoline direct injection (GDI) injector is an important parameter in the spray development process. Because the air flow path could be changed according to the spray and step hole dimensions. Moreover, CFD simulation was conducted by Star-CCM+ 13.06 in order to find out about air recirculation phenomenon. [ABSTRACT FROM AUTHOR]

A numerical study has been carried out to understand the effects of Unsteady Reynolds Averaged Navier-Stokes (standard k ― ε and RNG k ― ε model) and large eddy simulations (LES) on a multi-hole gasoline direct injection (GDI) system. The fuel injector considered in this study is the Spray G nozzle from the Engine Combustion Network (ECN). A blob injection model, based on empirical rate of injection (ROI) profile, is considered in this study. The latest data on spray penetrations from Engine Combustion Network is used for model validation along with experimental findings on suction velocity and local droplet diameter. The spray breakup is simulated by using the KH-RT breakup length model. The turbulence model constant Cε1, is tuned to match with the experimental data of liquid and vapor penetrations in simulations while using the standard k-ε turbulence model. On the other hand, the Kelvin-Helmholtz breakup model time constant (B1) and Rayleigh Taylor breakup length constant (Cbl) are tuned for the RNG k ― ε turbulence model. From this work it is observed that by increasing the breakup length model constants (Cbl), the radial dispersion of the spray increases, and the extent of breakup is lowered. The set of optimized model parameters used with RNG k - ε is also used for LES modeling studies with different sub-grid models. The spray penetrations with standard k ― ε turbulence (Cε1=1.44) model are reported underpredicting, and the RNG k ― ε and LES sub-grid models predicted well with the latest and recommended data from ECN. In terms of gas axial velocity comparison, the standard k-ε(Cε1=1.44) simulation setup does not perform as well as the simulation setups using RNG k-ε and LES turbulence models (with breakup parameters: Cbl = 16 and B1 = 32). However, the standard k-ε(Cε1=1.44) simulation setup perform better than the simulation setups using RNG k-ε and LES turbulence models (with breakup parameters: Cbl = 16 and B1 = 32) when it comes to predicting local droplet diameter at 15 mm downstream of the injector tip. A parametric study is also performed considering the geometry of the stepped holes in the computational domain. The rate of injection based simulation is initiated at the end of the smaller hole. The case including the stepped holes led to over-prediction compared to the case with the usual computational domain (i.e., without the stepped holes), in terms of spray penetrations, but exhibited higher levels of fluctuations in the spray morphology. Finally, parametric studies were carried out to understand the relative importance of the individual spray sub-models (breakup, evaporation and collision) and the results are conclusive that for a spray simulation the breakup models are the dominant factors.

The cylinder head assembly from a GDI engine was separated to build a GDI fuel injection system capable of controlling the rail pressure and fuel injection levels. The GDI fuel injection system is driven by a three-phase AC motor with a direct connection between the camshaft and the motor. The operating conditions of the GDI fuel injection system are equivalent to those of actual engine driving. The AC motor drives the GDI high-pressure fuel pump by rotating the engine camshaft. In the GDI high-pressure fuel pump (HPFP), fuel is pressurized on the upward stroke of the plunger and pumped to the fuel rail. Fuel rail pressure (FRP) control is possible by controlling the opening/closing timing of the HPFP's pressure control valve (PCV), the fuel injection duration and the camshaft speed. In order to calculate the fuel injection rate characteristics of the GDI injector statistically under fixed conditions of the camshaft speed, FRP, and injection duration, the measurements of the fuel injection rate were repeated at regular time intervals. To calculate the variation of the fuel injection rate, the S/N (signal-to-noise) ratio, which is the average FRP divided by the FRP standard deviation, was calculated. A fuel injection rate was obtained under 88 experimental conditions combining the three conditions of the HPFP's PCV opening/closing timing, fuel injection duration, and camshaft rotational speed. The smaller S/N ratio shows the larger FRP variation. Also, it was identified that the S/N ratio is related to the variation of the fuel injection rate. [ABSTRACT FROM AUTHOR]

• Optical extinction-based tomography showed good agreement with X-ray radiography result. • E00 showed strong plume collapse even under G3 condition (1 bar, 60 ℃). • LES simulation revealed indication of preferential evaporation in E00 spray. • E00 had 4 μm larger droplet diameter (averaged) than IC8. As modern gasoline direct injection (GDI) engines utilize sophisticated injection strategies, a detailed understanding of the air-fuel mixing process is crucial to further improvements in engine emission and fuel economy. In this study, a comprehensive evaluation of the spray process of single-component iso-octane (IC8) and multi-component gasoline surrogate E00 (36 % n-pentane, 46 % iso-octane, and 18 % n-undecane, by volume) fuels was conducted using an Engine Combustion Network (ECN) Spray G injector. High-speed extinction, schlieren, and microscopy imaging campaigns were carried out under engine-like ambient conditions in a spray vessel. Experimental results including liquid/vapor penetration, local liquid volume fraction, droplet size, and projected liquid film on the nozzle tip were compared under ECN G1 (573 K, 3.5 kg/m3), G2 (333 K, 0.5 kg/m3), and G3 (333 K, 1.01 kg/m3) conditions. In addition to the experiments, preferential evaporation process of the E00 fuel was elucidated by Large–Eddy Simulations (LES). The three-dimensional liquid volume fraction measurement enabled by the computed tomographic reconstruction showed substantial plume collapse for E00 under the G2 and G3 conditions having wider plume growth and plume-to-plume interaction due to the fuel high vapor pressure. The CFD simulation of E00 showed an inhomogeneity in the way fuel components vaporized, with more volatile components carried downstream in the spray after the end of injection. The high vapor pressure of E00 also results in ∼4 μm smaller average droplet diameter than IC8, reflecting a higher rate of initial vaporization even though the final boiling point temperature is higher. Consistent with high vapor pressure, E00 had a wider plume cone angle and enhanced interaction with the wall to cover the entire surface of the nozzle tip in a film. However, the liquid fuel underwent faster evaporation, so the final projected tip wetting area was smaller than the IC8 under the flash-boiling condition. [Display omitted] [ABSTRACT FROM AUTHOR]

Both the EU and China are evaluating the feasibility of lowering the detection limit of particle number (PN) measurement to 10 nm in future legislations, making it necessary to better understand the sub-23 nm particle emission characteristics from state-of-the-art vehicles. In this study, solid PN emissions with a diameter larger than 10 nm and 23 nm (known as SPN10 and SPN23) were compared over the WLTC, RTS95, and a so-called “worst-case” real driving emission (RDE) cycle (highly dynamic/0 °C) using two certification-level particle number counters (PNCs) employing evaporation tube (ET) and catalytic stripper (CS) as volatile particle remover (VPR). The results show that SPN10 emissions were 31.7%, 27.8%, and 15.2% higher than SPN23 over the WLTC, RTS95, and laboratory RDE cycles. Sub-23 nm particles were almost not identified within the engine cold-start phase and tended to be a hot-running pollutant favored by aggressive driving styles (frequent accelerations and high engine loads), fuel-cut during decelerations, and long idles. Lower testing temperature delayed the light-off of catalyst and, therefore, significantly reduced the formation of sub-23 nm particles within the engine warm-up stage. Lowering the detection limit to 10 nm is deemed to provide more public health protection since it will guide manufacturers to pay more attention to vehicle hot-running emissions.

An experimental system was developed to evaluate the fuel injection parts of a gasoline direct injection engine. An AC motor and an inverter were used to rotate the camshaft in the engine cylinder head. A single plunger high-pressure fuel pump (HPFP) driven by a square cam at the end of the camshaft was used in the gasoline direct injection engine. The rotation position of the square cam was measured by a rotary encoder. The developed system allows control of the camshaft rotation speed, the HPFP pressure control valve (PCV) opening and closing timing, and the fuel injection duration, which are three important factors affecting the fuel rail pressure (FRP). It is confirmed that the fuel rail pressure can be made to vary wit different combinations of these three factors. By using the experimental system developed in this study, the fuel rail pressure can be effectively controlled in the range of 3 MPa to 20 MPa. The most influential factor for control of the fuel rail pressure was the HPFP PCV opening and closing timings. With the proposed using the experimental system, the rail pressure, fuel rail pressure wave characteristics, and the injector drive characteristics can all be assessed under various fuel injection conditions. [ABSTRACT FROM AUTHOR]

The fuel octane number affects the fuel consumption and emission characteristics of vehicles powered by spark-ignition engines. An investigation on the effects of commercial types of gasoline with different research octane numbers (RON) on a vehicle's performance can provide valuable insights and guidelines for the further improvement of the engine and fuel design. In this work, three commercial-types of gasoline with RON values of 92, 95, and 98 were tested in two compact passenger vehicles. One vehicle is equipped with a gasoline direct injection (GDI) engine with a 1.4-L displacement and a turbocharging system, and the other one is equipped with a port fuel injection (PFI) naturally-aspired engine with a 1.6-L displacement. The new European drive cycle (NEDC) was used to test the effects of three gasoline fuels on both vehicles. The experimental results show that for the vehicle equipped with the GDI engine, with the increase of the RON number, the fuel consumption, carbon dioxide (CO2), and carbon monoxide (CO) emissions increase first and then decrease. The total hydrocarbon (THC) and particulate matter (PM) emissions decrease first and then increase, while the NOx emissions increase gradually; the differences between the maximum and minimum values in the fuel consumptions and the emissions of NOx, CO, THC, CO2 , and PM are 0.1 L/100 km (1.7%), 57.54 mg/km (4.5%), 119.26 mg/km (3.3%), 21.73 mg/km (2.3%), 2.55 g/km (2.0%), and 0.24 mg/km (20.6%), respectively. For the vehicle with the PFI engine, with the increase of the RON number, the fuel consumption decreases, the CO2 and THC emissions decrease first and then increase, and the CO emission increases first and then decreases, while the NOx and PM emissions increase gradually; the differences between the maximum and minimum values of the fuel consumptions and the emissions of NOx, CO, THC, CO2 , and PM are 0.18 L/100 km , 18.19 mg/km (1.1%), 84.82 mg/km (1.6%), 21.06 mg/km (3.1%), 1.36 g/km (0.9%), and 0.47 mg/km (50.9%), respectively. It can be seen that different RONs lead to the variation in fuel consumption and emissions in an NEDC test. In terms of acceleration performance, the impact of different fuels is considered to be only marginal because the variation in the acceleration time due to fuel effects is less than 2%. [ABSTRACT FROM AUTHOR]

With the wide application of gasoline direct injection system, its noise problem is becoming increasingly prominent under serious competitive environment. As the primary noise source of the engine in idle condition, the significant noise generated by the low-to-high pressure transmission part of high-pressure fuel pump becomes more and more serious. This paper focuses on the driving component of high-pressure fuel pump, the roller tappet, and experimentally studies effect factors of impact noise induced by it at engine idle. Both the impact occurrence time and position are analyzed from the combined vibration acceleration and crankshaft/camshaft rotation angle signals in the time domain according to the structure and kinematic mechanism of the roller tappet. The influences of the axial clearance between roller and tappet shell, the engine rotation speed and the lubrication conditions are investigated by experiments. The experimental results show that the lubrication is the primary factor for the roller tappet induced impact noise reduction. A significant improvement about 83% can be achieved under pressure lubrication. [ABSTRACT FROM AUTHOR]

The nanoparticles (NP) count concentrations are limited in EU for all Diesel passenger cars since 2013 and for gasoline cars with direct injection (GDI) since 2014. For the particle number (PN) of MPI gasoline cars there are still no legal limitations. In the present paper some results of investigations of nanoparticles from five DI and four MPI gasoline cars are represented. The measurements were performed at vehicle tailpipe and in CVS-tunnel. Moreover, five variants of “vehicle – GPF” were investigated. The PN-emission level of the investigated GDI cars in WLTC without GPF is in the same range of magnitude very near to the actual limit value of 6.0 × 10^12 1/km. With the GPF’s with better filtration quality, it is possible to lower the emissions below the future limit value of 6.0 × 10^11 1/km. The modern MPI vehicles also emit a considerable amount of PN, which in some cases can attain the level of Diesel exhaust gas without DPF and can pass over the actual limit value for GDI (6.0 × 10^12 1/km). The GPF-technology offers in this respect further potentials to reduce the PN-emissions of traffic.

Highlights • This study analyzed the on-road PN emissions characteristics of a GDI vehicle. • PN emissions during the cold start phase accounted for a significant portion. • The CS effect on the decrease of PN emissions was 36 % in the total trip sections. • The GPF effect on the reduction of PN emissions was 45 % in the total trip sections. Abstract Particle number (PN) emissions must be below 9.0 × 1011 #/km according to the Euro 6d regulation with a conformity factor (CF) of 1.5 during a real driving emissions (RDE) test, including the cold start phase. Thus, the object of this study is to analyze the on-road PN emissions characteristics under a cold start condition of a gasoline direct injection (GDI) vehicle depending on a catalytic stripper (CS), a gasoline particulate filter (GPF), the cold start phase, and the trip section using a corona charger type particle sensor, a CS, and an exhaust flow meter. Because the fuel-rich mode and retarded injection timing were applied to compensate for engine instability and caused incomplete combustion and deterioration of fuel vaporization during the cold start phase, PN emissions during the cold start phase accounted for a significant portion of the total PN. On-road PN emissions for the total trip were 2.71 × 1012 (without CS and GPF), 1.72 × 1012 (with CS and without GPF), 1.47 × 1012 (without CS and with GPF) and 9.50 × 1011 (with CS and GPF) #/km for cases A, B, C and D, respectively. The average CS effects on the decrease of PN emissions were 35.4% and 32.2% in the urban, 52.2% and 63.4% in the rural, 22.8% and 88.6% in the motorway, and 36.5% and 35.6% in the total trip sections without and with GPF, respectively. The average GPF effects on the reduction of PN emissions were 42.7% and 39.9% in the urban, 58.2% and 68.0% in the rural, 27.9% and 89.3% in the motorway, and 45.6% and 44.8% in the total trip sections without and with CS, respectively. [ABSTRACT FROM AUTHOR]

In this study, a plunger-type high-pressure fuel pump is designed for use in a Gasoline Direct Injection (GDI) system and intended to retrofit onto small spark ignition (SI) engines of less than 0.2 liter/cylinder. The pump is developed to generate high-pressurized fuel in range of 4-20 MPa, and is capable of supplying fuel transfer of 10-20 g/s. SolidWorksTM software was extensively used in the analysis to design the pump via 3D modeling approach. The designed model was then analyzed using ANSYS FluentTM software to simulate for the flow pattern as well as the pressure distribution in the pump cavity during pumping process. The concept, design geometry, calculation and the testing method employed for the high-pressure fuel pump are discussed in this paper. This research aims to design a high-pressure fuel pump used in small spark ignition engines applications wherein to improve the efficiency of the engine, the fuel pump is driven by an external DC motor, relieving the engine in providing the auxiliary power supply. In general based on the simulation, during pumping process at 1000 RPM (using the two cam lobe design), the pump is able to supply fuel at 6.00 MPa of the discharge pressure. The fuel was able to be delivered by as much as 0.0196 kg/s, at a travelling velocity of 3.8 m/s, in which this is well in the range of the initial pump design requirements. [ABSTRACT FROM AUTHOR]

As idle condition in gasoline direct injection (GDI) engines always has high particulate number (PN) issue, the effects of coolant temperature coupled with controlling strategies on PN emission has been experimentally studied. Two sets of experiments have been conducted to make a comprehensive understanding. The first set is aimed to analyze ignition timing and excess air ratio characteristics, and the second one mainly investigates injection strategies. The experimental results indicate that the total PN declines with increased coolant temperature. When coolant temperature exceeds 70 °C, PN dramatically decreases. 5–22 nm PN emissions increase and 22–50 nm PN emissions decrease with higher λ. Besides, richer mixture has higher 50–150 nm PN than leaner ones. Properly advanced ignition timing will decrease total PN under idle stage and the decrement is mainly from 5 to 22 nm particles. The total PN minimizes at 5 MPa injection pressure, which can fulfill fuel evaporation and restrict nucleation process simultaneously. The total PN minimizes at 80 CAD BTDC injection timing, which is only 14% of the minimum value in 140 CAD BTDC. Thus, coolant temperature has crucial effect on PN emissions and optimizing other operating parameters will further reduce PN. [ABSTRACT FROM AUTHOR]

This study investigates fuel sprays of light naphtha (LN), primary reference fuel (PRF) and gasoline under different ambient pressures with an outwardly opening piezo gasoline direct injection (GDI) fuel injector. The tested gasoline fuel (regular grade with up to 10% ethanol, E10) was obtained by mixing fuels with AKI (the average of the research octane number (RON) and the motor octane number (MON)) of 87 from three local gas stations. Primary reference fuel (PRF) is commonly used as gasoline surrogate fuel and is blended by iso -octane and n-heptane. PRF95 is the blend of 95% iso -octane and 5% n-heptane by volume. LN fuel was provided by Saudi Aramco Oil Company. Five different ambient pressure conditions varied from 1 bar to 10 bar were tested. The spray was visualized by applying a Mie-scattering technique and a high-speed camera was employed to capture the spray images. The spray structure, spray angle, spray penetration length and spray front fluctuation were analyzed and compared among three fuels. Spray images show that a clear filamentary hollow-cone spray structure is formed for all three fuels at atmospheric conditions, and toroidal recirculation vortexes are observed at the downstream spray edges. A higher ambient pressure leads to a stronger vortex located closer to the injector outlet. Generally speaking, larger spray angles are found under higher ambient pressure conditions for all three fuels. Gasoline fuel always has the largest spray angle for each ambient pressure, while PRF95 has the smallest at most time. For each fuel, the spray front penetration length and spray front penetration velocity decrease with increasing ambient pressure. LN, PRF95 and gasoline show similar penetration length and velocity under the tested conditions. A two-stage spray front fluctuation pattern is observed for all three fuels. Stage one begins from the start of the injection and ends at 450–500 μs after the start of the injection trigger (ASOIT) with a slow fluctuation increase for all ambient conditions. After Stage one, the spray front fluctuation increases rapidly to a certain level and then becomes stable in Stage two. [ABSTRACT FROM AUTHOR]

The particulate matter (PM) emissions of gasoline vehicles were much lower than those of diesel vehicles until the introduction of diesel particulate filters (DPFs) in the early 2000s. At the same time, gasoline direct injection (GDI) engines started to become popular in the market due to their improved efficiency over port fuel injection (PFI) ones. However, the PM mass and number emissions of GDI vehicles were higher than their PFI counterparts and diesel ones equipped with DPFs. Stringent PM mass levels and the introduction of particle number limits for GDI vehicles in the European Union (EU) resulted in significant PM reductions. The EU requirement to fulfill the proposed limits on the road resulted to the introduction of gasoline particulate filters (GPFs) in EU GDI models. This review summarizes the evolution of PM mass emissions from gasoline vehicles placed in the market from early 1990s until 2019 in different parts of the world. The analysis then extends to total and nonvolatile particle number emissions. Care is given to reveal the impact of ambient temperature on emission levels. The discussion tries to provide scientific input to the following policy-relevant questions. Whether particle number limits should be extended to gasoline PFI vehicles, whether the lower limit of 23 nm for particle number measurements should be decreased to 10 nm, and whether low ambient temperature tests for PM should be included.

A turbocharged Gasoline Direct Injection (GDI) engine fueled by n -butanol/gasoline blends is studied under the condition of wide-open throttle (WOT) in this paper. The effects of high n -butanol content (30% and 50% n -butanol by volume, i.e. Bu30 and Bu50) on the thermodynamic process and fuel efficiency of the GDI engine are discussed, as well as the engine emissions. Also, the results are compared with RON 93 gasoline and 10% ethanol/gasoline blended fuel (E10), which have been widely used in cars. The results show that high content of butanol addition can be realized in the GDI engine without any modification to its structure and control. Moreover, the maximum BMEP of the engine can increase to 1.99 MPa with Bu50. As compared with the gasoline and E10, high n -butanol/gasoline blends increase in-cylinder combustion pressure and pressure rise rate, promote ignition, and shorten burning duration. What is more, high n -butanol/gasoline blends improve combustion stability and decrease exhaust temperature, but they cannot deteriorate anti-knock quality. However, high n -butanol/gasoline blends increase Brake Specific Fuel Consumption (BSFC), and they decrease combustion efficiency and Brake Thermal Efficiency (BTE) at WOT. As for the engine emissions, high n -butanol/gasoline blends increase UHC and CO emissions but reduce NOx and CO 2 emissions. The study implies that 0–50% butanol/gasoline blends can directly replace the existing engines fueled with regular RON 93 gasoline or E10. [ABSTRACT FROM AUTHOR]

Characterization of the spray angle, penetration, and droplet size distribution is important to analyze the spray and atomization quality. In this paper, the spray structure development and atomization characterization of two naphtha fuels, namely light naphtha (LN) and whole naphtha (WN) and two reference fuel surrogates, i.e. toluene primary reference fuel (TPRF) and primary reference fuel (PRF) were investigated using a gasoline direct injection (GDI) fuel injector. The experimental setup included a fuel injection system, a high-speed imaging system, and a droplet size measurement system. Spray images were taken by using a high-speed camera for spray angle and penetration analysis. Sauter mean diameter, Dv(10), Dv(50), Dv(90), and particle size distribution were measured using a laser diffraction technique. Results show that the injection process is very consistent for different runs and the time averaged spray angles during the measuring period are 103.45°, 102.84°, 102.46° and 107.61° for LN, WN, TPRF and PRF, respectively. The spray front remains relatively flat during the early stage of the fuel injection process. The peak penetration velocities are 80 m/s, 75 m/s, 75 m/s and 79 m/s for LN, WN, TPRF and PRF, respectively. Then velocities decrease until the end of the injection and stay relatively stable. The transient particle size and the time-averaged particle size were also analyzed and discussed. The concentration weighted average value generally shows higher values than the arithmetic average results. The average data for WN is usually the second smallest except for Dv90, of which WN is the biggest. Generally the arithmetic average particle sizes of PRF are usually the smallest, and the sizes does not change much with the measuring locations. For droplet size distribution results, LN and WN show bimodal distributions for all the locations while TPRF and PRF shows both bimodal and single peak distribution patterns. The results imply that droplet size distribution is skewed to the larger side for locations close the axis and is skewed to the smaller side for distance away from the axis. [ABSTRACT FROM AUTHOR]

Sub-23 nm particulate emissions from internal combustion engines have become a topic of interest for research and legislative regulations in recent years. Many studies focused on electrical mobility measurements of soot particles, but few works employed additional techniques that do not rely on equivalent diameters. In this work, exhaust-sampled soot from a 1.0 L gasoline direct injection engine was analysed by transmission electron microscopy (TEM). Three operating conditions were assessed: 1500 rpm fast-idle, 1500 rpm with 40 Nm and 1750 rpm with 20 Nm brake torque. A distinct mode of sub-10 nm particulates was found equally distributed on some sections of the TEM grids for all three conditions. These particulates appeared to be stable under the electron beam, suggesting a non-volatile nature. Differential mobility spectrometer measurements with and without catalytic stripper suggested the presence of volatiles but also indicated high levels of solid sub-23 nm particulates. Furthermore, more fractal soot agglomerates consisting of several primary particles were also observed by TEM. The nanostructure of primary particles exhibited mainly core-shell nanostructures for all operating conditions. An additional amorphous layer was observed surrounding primary particles for 1500 rpm fast-idle. Amorphous particulates and crystalline regions in agglomerates were identified for 1750 rpm with 20 Nm brake torque. Fringe analysis of the nanostructures was conducted for all three samples, with preliminary findings indicating similar fringe lengths of ca. 1.04 nm and tortuosity values of around 1.16. [ABSTRACT FROM AUTHOR]

• Effects of needle behavior on fuel flow rate of GDI injectors were analyzed. • The movement of armature and ball was quantitatively analyzed through the X-ray visualization. • Flow rate of the second injection gradually increased as dwell time was shortened. To meet strong emission regulations such as Euro-7, which is expected to be implemented in 2025. The multiple-injection strategy is one of well-known solutions to reduce exhaust gas and improve combustion performance on GDI engine. In order to realize multiple-injection strategy, it is necessary to secure excellent flow rate repeatability within short period. Therefore, the purpose of this study was to analyze the flow rate repeatability of GDI injector under various multiple injection conditions and to correlate with needle behavior of GDI injector and flow rate repeatability. To analyze flow rate repeatability, the injection rate data was obtained by the Bosch method and the individual flow rates of 110 shots were analyzed under several experimental conditions. The movements of the ball and armature inside the injector were visualized using the X-ray phase contrast imaging (XPCI) technique, and the individual behaviors of the ball and the armature were quantitatively analyzed by image post-processing analysis. In this study were used two test GDI injectors with same structure. Whereas Flow rate results were different on shorter dwell time conditions. This study revealed that a specific injector had unstable injection rate and worse Shot to Shot (STS) deviation under dwell time 0.7 ms. In addition, armature bouncing appeared in a specific GDI injector. This armature bouncing affects unstable flow rate characteristics because when armature lift up again, the position of armature was different at every time. [ABSTRACT FROM AUTHOR]

Engine start-stop (S&S) technology has been substantially incorporated into modern vehicles to save fuel during idling in congested urban areas because fuel economy regulations have become more stringent. However, the potential for increasing particle emissions after engine restarts, especially in cold environments, is of great concern. To investigate the effects of S&S systems on fuel consumption and tailpipe emissions, a chassis dynamometer was employed to measure the fuel consumption, particulate matter (PM), solid particle number (PN), particle number size distribution and black carbon (BC) for a typical gasoline direct injection vehicle when the S&S was on (S&S-on) and when the S&S was off (S&S-off) according to the worldwide harmonized light-duty test cycle in both hot (28 °C) and cold (5 °C) environments. S&S operation resulted in 3.1–4.3% fuel-savings at 28 °C but had a tendency to increase particulate emissions, especially of BC (21.8–31.8%) and PM (19.2–32.8%). Although PN emissions with S&S-on over the entire cycle were slightly lower than those with S&S-off, more particles were emitted during the engine restart moments. In a cold environment, the fuel-savings advantage of the S&S system was weakened, and the negative impacts on the particle emissions during the restart moment worsened. The S&S system resulted in higher abundances of accumulation mode particles, especially under cold ambient conditions. The relationship between the PN reduction rates and idling segments was determining to be exponential. Our results indicate that the S&S system, which may increase particle emissions during restarts, does save fuel, and that a comprehensive evaluation of the system in cold environments is needed to determine the serviceability of new engine technologies and after-treatments. [Display omitted] • The advantages of start-stop system (S&S) decrease in cold environments. • S&S operation uses 3.1–4.3% less gasoline at 28 °C, but increases particle emissions. • More large particles (>0.07 μm) are generated during engine restart moments. • Engine restarts with S&S-on result in more particles at 5 °C than at 28 °C. • Particles emitted during restart with S&S-on decrease as the idling time increases. [ABSTRACT FROM AUTHOR]

• Spray collapsing of using a practical lateral-mounted gasoline direct injector were investigated. • High-speed diffusive back illumination extinction imaging and computed tomography reconstruction were applied. • Spray collapse and plume merging showed significant transient behavior. • The triangular spray pattern was found to be prone to merging of centrally located plumes and spray collapse. Spray collapsing and plume merging processes were investigated using a lateral-mounted gasoline direct injection (GDI) injector with a practical 'triangular' spray pattern. High-speed diffusive back illumination extinction imaging followed by computed tomography reconstruction was applied to understand the spatiotemporal plume dynamics under engine-like conditions. The spray chamber and injector conditions include (1) cold, subcooled standard temperature and pressure (STP) used by the injector manufacturer, (2) practical gasoline fuels with full-range distillation, (3) flash-boiling with fuel temperature and vacuum gas pressure, and (4) high gas pressure and temperature typical of injection during compression. The novel experiments permit tracking of plume merging at different times and axial distances downstream of the nozzle. A triangular 6-hole pattern, which is widely used in lateral-mounted GDI engines, was found to be prone to having the centrally located plumes move close to each other thus leading to spray collapse with these plumes at all practical test conditions (2)–(4). Variations of air entrainment and local pressure with different conditions were identified as dominant factors for the timing and position of spray collapse. [ABSTRACT FROM AUTHOR]

To obtain the precise injection in GDI engines, this paper presents a model-based rail pressure control scheme. First, a mathematical model is derived for the fuel rail injection system based on hydrodynamics and the bulk modulus of elasticity and simplified reasonably for the controller design. The system is uncontrollable at the point where the pump pressure is equal transiently to the rail pressure. A simple controller is designed for driving the system to the regular case where the pump pressure is larger than the rail pressure. In order to deal with system nonlinear, a nonlinear controller is derived and rearranged in the structure of feedforward feedback. The feedforward is related to the reference dynamics and the gain is state-dependent, while the feedback includes a state-dependent PD/PID error feedback and a state feedback related to the characteristics of the fuel rail system. The structure of the controller benefits potentially to the engineering-oriented implementation. Second, robustness is analyzed in the framework of input-to-state stability, where the error induced from the controller implementation, disturbances, and uncertainties are lumped as an additive input. Finally, the designed control scheme is tested in the more realistic simulation model established in the AMESim environment and the results are satisfying. [ABSTRACT FROM PUBLISHER]

Abstract: The light intensity measurement and image visualization of multi-hole injection spray due to different hole arrangements and hole numbers were investigated. The light intensities and behavior characteristics of the GDI spray were analyzed through the axial and diagonal spray penetration, cone angle, and spray area from the spray images by using the image visualization system and image analysis system. The atomization performance of GDI injectors was analyzed by the local and overall Sauter mean diameter (SMD) measurement. It is revealed that the higher injection pressure shows higher light intensity levels due to the strong vortices and collision by a high injection pressure. The light intensity level at the outer and end region of the spray shows lower value compared to that at the center spray region. In all of test injectors, the increased injection pressure leads to the decrease of the droplet size distribution in the initial spray. But, there is little difference of the droplet size at low and high injection pressure in middle and latter period after the injection. The overall SMD of GDI injectors showed from 14 to 23.14μm. [Copyright &y& Elsevier]

Abstract: Exhaust gas fuel reforming has been identified as a thermochemical energy recovery technology with potential to improve gasoline engine efficiency, and thereby reduce CO2 in addition to other gaseous and particulate matter (PM) emissions. The principle relies on achieving energy recovery from the hot exhaust stream by endothermic catalytic reforming of gasoline and a fraction of the engine exhaust gas. The hydrogen-rich reformate has higher enthalpy than the gasoline fed to the reformer and is recirculated to the intake manifold, i.e. reformed exhaust gas recirculation (REGR). The REGR system was simulated by supplying hydrogen and carbon monoxide (CO) into a conventional EGR system. The hydrogen and CO concentrations in the REGR stream were selected to be achievable in practice at typical gasoline exhaust temperatures. Emphasis was placed on comparing REGR to the baseline gasoline engine, and also to conventional EGR. The results demonstrate the potential of REGR to simultaneously increase thermal efficiency, reduce gaseous emissions and decrease PM formation. [Copyright &y& Elsevier]

Highlights: [•] We obtain distribution of droplet velocity and diameter using PDPA system. [•] Transition of a jet break-up processes is visualized using Nd:Yag sheet laser system. [•] Elevated injection pressure can activate a jet break-up processes. [•] A limit in injection pressure to enhance droplet atomization is observed. [Copyright &y& Elsevier]

Highlights: [•] Performance of a diesel engine using direct-injection ammonia-DME is investigated. [•] Stable engine operation can be achieved by using early injection timings. [•] Combustion of high concentration of ammonia exhibits HCCI characteristics. [•] High load operations favor the use of high concentration of ammonia. [ABSTRACT FROM AUTHOR]

• Injection rate and solenoid voltage of GDI injectors were measured. • Regression model was derived using an artificial neural network. • The injection rate model well predicted non-linear behaviors of the injection rate. • The solenoid voltage model showed good agreement with the measured signal. Current state-of-the-art gasoline direct-injection (GDI) engines use multiple injections as one of the key technologies to improve exhaust emissions and fuel efficiency. For this technology to be successful, secured adequate control of fuel quantity for each injection is mandatory. However, nonlinearity and variations in the injection quantity can deteriorate the accuracy of fuel control, especially with small fuel injections. Therefore, it is necessary to understand the complex injection behavior and to develop a predictive model to be utilized in the development process. This study presents a methodology for rate of injection (ROI) and solenoid voltage modeling using artificial neural networks (ANNs) constructed from a set of Zeuch-style hydraulic experimental measurements conducted over a wide range of conditions. A quantitative comparison between the ANN model and the experimental data shows that the model is capable of predicting not only general features of the ROI trend, but also transient and non-linear behaviors at particular conditions. In addition, the end of injection (EOI) could be detected precisely with a virtually generated solenoid voltage signal and the signal processing method, which applies to an actual engine control unit. A correlation between the detected EOI timings calculated from the modeled signal and the measurement results showed a high coefficient of determination. [ABSTRACT FROM AUTHOR]

Highlights: [•] CAI combustion is achieved in a 2-stroke poppet valve GDI engine. [•] Gasoline and its mixture with ethanol are used as the fuel on the engine. [•] The effect of ethanol content on operating range, combustion and emissions are analysed. [ABSTRACT FROM AUTHOR]

Abstract: Two Euro 4 gasoline passenger vehicles (one gasoline direct injected vehicle and one port fuel injected vehicle) were tested over the cold start New European Driving Cycle (NEDC). Each vehicle was respectively fueled with gasoline and M15 methanol gasoline. Particle number concentrations were measured by the electrical low pressure impactor (ELPI). Particle masses were measured by gravimetric method and estimated from the number distributions using two density distributions (one is constant with the particle size and one is power law related with the size). The first 7 stages of ELPI were used for estimation. The results show that for each vehicle, PM masses measured by gravimetric method, the total PM numbers measured by ELPI and estimated PM masses for M15 are lower than those for gasoline. For each kind of fuel, PM masses by two methods and total PM numbers from the GDI vehicle are higher than those from the PFI one. PM number distribution curves of the four vehicle/fuel combinations are similar. All decline gradually and the maximum number of each curve occurs in the first stage. More than 99.9% numbers locate in the first 8 stages of which diameters are less than 1μm. PM number emissions correlate well with the acceleration of the two vehicles. The estimated particle masses were much lower than the gravimetric measurements. [Copyright &y& Elsevier]

The reduction of combustion emissions and fuel consumption can be achieved by controlling the fuel mixture to be burned and therefore the fuel injection. In this study a gasoline direct injection (GDI) piezo hollow cone injector is investigated by visualization measurements. Both single and double injection events are examined in a pressurized chamber. For the single injection, the influence of the ambient temperature and pressure is analysed in detail. For the double injection, the ambient conditions and the time interval between two injections are varied. For the single injection, the general shape of the spray, the recirculation eddy formed at the spray edge, the stringy structure of the hollow cone, and defined quantities such as the penetration length or the spray width are examined with respect to the influence of the ambient conditions. For the double injection, the same properties are evaluated, with the focus put not only on the influence of the ambient conditions, but also on the mutual interaction of two spray events. The experimental results show a clear impact of both the ambient conditions and the time difference between two injections. In particular, the investigation of the recirculation eddy may be helpful in determining possible positions for the spark plug, since the spark plug is preferably placed in regions where the air-fuel mixture variations are minimal. [ABSTRACT FROM AUTHOR]

• The evaporation process after start of injection is divided into three stages according to evaporation ratio. • The difference in the spray evaporation ratio of the two injectors mainly appeared before the spray collapse. • Before and after the spray collapse, the position where the spray evaporates greatly changes. Spray evaporation characteristics have an important influence on air-fuel mixing and the optimization of combustion to achieve high performances and ultra-low emissions. This study aims to compare and analyze the evaporation characteristics of five-hole gasoline direct injection injectors with different hole arrangements under flash-boiling conditions. The holes of two injectors are arranged as a pentagon. The hole arrangement of injector A (standard type) is similar to a regular pentagon, whereas two holes on the sides of the pentagon corresponding to injector B (skew type) are shifted toward the inside and bottom of the pentagon. In this study, Schlieren and Mie-scattering techniques are used to visualize the evaporation of spray. Although this method is difficult to extract the vapor area from the vapor-liquid mixing zone, it can accurately calculate the area of the pure evaporation zone by subtracting the area of the liquid phase mixing zone from the global area. Therefore, this study compared the spray evaporation characteristics of the two injectors relatively, by calculating the area of the pure evaporation zone. Experiments were compared with different injector directions (0° and 90°) and under a wide range of superheat conditions (0°C–130 °C). Only a slight difference is found between the evaporation characteristics of the standard- and skew-type injectors in the 0° direction. However, in the 90 direction, before the spray collapses, the larger plume spacing of the skew-type injector, determined by the injector hole arrangement, promotes air-flow in the spray center, leading to larger evaporation ratio. After the spray collapses, the spray structure difference caused by the hole arrangement is reduced, and the two injectors exhibit similar evaporation characteristics. [Display omitted] [ABSTRACT FROM AUTHOR]

Controlled auto-ignition (CAI) combustion, also known as homogeneous charge compression ignition (HCCI) can be achieved by trapping residuals with early exhaust valve closure in both port and direct fuel injection four-stroke gasoline engines. A multi-cycle three-dimensional engine simulation program has been developed and applied to study the effect of injection on in-cylinder mixing and CAI combustion. The full engine cycle simulation, including complete gas exchange and combustion processes, was carried out over several cycles in order to obtain the stable cycle for analysis. The combustion models used in the present study are based on the Shell auto-ignition model and the characteristic-time combustion model, both of which have been modified to take the high level of residual gas into consideration. A liquid sheet break-up spray model was used for the droplet break-up processes. The analyses show that the injection timing plays an important role in affecting the in-cylinder air/fuel mixing and mixture temperature, which in turn affects the CAI combustion and engine performance. In comparison with the port fuel injection case, an early direct injection at exhaust valve closure can lead to higher load and lower fuel consumption. [ABSTRACT FROM AUTHOR]

Gasoline direct injection (GDI) properties, including injection pressure (IP), injection timing (IT) and injection angle (IA), have critical impacts on the cycle to cycle combustion variation that directly determines the long term stable operation for free piston linear generator (FPLG) with dual cylinder configuration. Therefore, in this present paper, the spray characteristics and combustion process of FPLG were explored through 9 cases that were designed by adopting orthogonal experimental method at different IP, IT and IA. Furthermore, the spray numerical model at different IP were validated with the spray experiment rig. The results displayed that, when at IT130°CA BTDC, the maximum cylinder pressure is 4.1 MPa and the mixture concentration is 0.98. However, at IT120°CA BTDC, the maximum cylinder pressure is 3.6 MPa and the mixture concentration is 0.94. Meanwhile, at IT100°CA BTDC, the maximum cylinder pressure only reaches 3 MPa and the mixture concentration is 0.86. The results indicated that the increase of IT can make the fuel take advantage of strong airflow movement, so as to improve the mixture uniformity. Thus, the combustion quality and power performance are enhanced. Moreover, at IP12MPa, when we define the maximum mixing uniformity as 1, the mixture uniformity reaches 0.98, 0.94 and 0.86 with IT130°CA BTDC, 120°CA BTDC, 100°CA BTDC, correspondingly. It is much higher than IP15MPa and IP7MPa, individually. It is can be explained by the interaction of high IP that can make fuel evaporation to form a mixture, thus reducing the fuel evaporation with the increase of penetration distance. In addition, IA has no obvious influence on the mixture uniformity, but reasonable IA could improve combustion quality within a certain range. [ABSTRACT FROM AUTHOR]

• Ball behavior inside injector was visualized and analyzed using X-ray technique. • Reducing the sac volume will decrease ball lift and shorten the closing delay. • Injectors with small sac volume have a greater advantage in reducing post-injection, but also have problems with larger ball deviation and longer STP. • Some proposals were made to optimize the design of injectors with smaller sac volume. The purpose of this study is to analyze the effect of sac-volume in high-pressure gasoline direct injection (GDI) injector on ball behavior, initial spray characteristics, and the post-injection after the end of injection. In this study, the advanced visualization technique, X-ray phase contrast imaging (XPCI), used to visualize and analyze the ball behavior inside the injector, and the initial spray behavior within several millimeter (mm) from the nozzle tip. Using XPCI and Mie-scattering techniques, the relationship between spray characteristics and the internal flow could be analyzed at injection pressures of 10 MPa and 35 MPa, for injection duration of 0.52 ms and 1.5 ms. Results showed that the ball was further away from the center of the nozzle when testing with a smaller sac volume. Regarding spray characteristics, smaller sac volume led to increased spray tip penetration due to a lower average ball lift. In addition, as the sac volume decreases, the amount of residual fuel discharged at the end of injection was less; additionally, ligaments and droplets formed were smaller. [ABSTRACT FROM AUTHOR]

• Hole length and step hole diameter affect plume interactions via width of the spray plumes. • Injector with smaller hole length and larger step hole diameter (Injector D) has the largest transition region length. • The spray has a uniform concentration distribution and shorter STP in the transition region. • Injector D exhibits better adaptability if the spray characteristics of the transition region are utilized in engine design. This investigation utilized four gasoline direct injection (GDI) injectors with different nozzle lengths and step hole diameters to analyze the influences of nozzle structure on the superheated plume and spray collapse under different superheat degrees. The spray behaviors of were recorded by using high-speed shadowgraphs. In addition, the spray concentration distribution, spray development, and spray swelling characteristics under different superheat conditions were analyzed. The experimental results showed that hole length and step hole diameter affected the widths of the spray plumes, which then affected the spray characteristics. Wider spray plumes enhance plume interactions and promote reduced spray penetration. This causes spray to enter the transition regime at a lower degree of superheat. In addition, the transition regime exhibits better spray characteristics than the subcooled and flare flash boiling regimes. Injector with smaller hole length and larger step hole diameter exhibits stronger adaptability while utilizing the remarkable spray characteristics in the transition regime, owing to the greater length of the spray transition regime. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The particulate matter (PM) emissions of gasoline vehicles were much lower than those of diesel vehicles until the introduction of diesel particulate filters (DPFs) in the early 2000s. At the same time, gasoline direct injection (GDI) engines started to become popular in the market due to their improved efficiency over port fuel injection (PFI) ones. However, the PM mass and number emissions of GDI vehicles were higher than their PFI counterparts and diesel ones equipped with DPFs. Stringent PM mass levels and the introduction of particle number limits for GDI vehicles in the European Union (EU) resulted in significant PM reductions. The EU requirement to fulfill the proposed limits on the road resulted to the introduction of gasoline particulate filters (GPFs) in EU GDI models. This review summarizes the evolution of PM mass emissions from gasoline vehicles placed in the market from early 1990s until 2019 in different parts of the world. The analysis then extends to total and nonvolatile particle number emissions. Care is given to reveal the impact of ambient temperature on emission levels. The discussion tries to provide scientific input to the following policy-relevant questions. Whether particle number limits should be extended to gasoline PFI vehicles, whether the lower limit of 23 nm for particle number measurements should be decreased to 10 nm, and whether low ambient temperature tests for PM should be included. [ABSTRACT FROM AUTHOR]