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Some experimental investigations have shown that the trade-off curve of NOx vs. particulate of a D.I. diesel engine with split-injection strategies can be shifted closer to the origin than those with a single-pulse injection, thus reducing both particulate and NOx emissions significantly. It is clear that the injection mass ratios and the dwell(s) between injection pulses have significant effects on the combustion and emissions formation processes in the D.I. diesel engine. However, how and why these parameters significantly affect the engine performances remains unexplained. The effects of both injection mass ratios and dwell between injections on vapor/liquid distributions in the split-injection diesel sprays impinging on a flat wall have been examined in our previous work.

Reduction of orifice diameter of nozzle is advantageous to the fuel atomization in a D.I. diesel engine. However, the diameter reduction is usually accompanied with decrease of spray tip penetration, thus worsening fuel spatial-distribution and fuel-air mixing. In this paper, a group-hole nozzle concept was proposed to solve the problem resulting from minimization of orifice diameter. Compared to the conventional multi-hole nozzle, group-hole nozzle has a series group of orifices, and each group consists of two micro-orifices with a small spatial interval and small angle. For examining the characteristics of the spray injected by the group-hole nozzle, the ultraviolet-visible laser absorption-scattering (LAS) imaging technique was adopted to determine vapor concentration and droplets density as well as other spray characteristics such as spray angle and penetration of both vapor and liquid phases.

Nowadays, transportation issues have been increasingly serious, and countries all over the world are actively exploring effective solutions. Intelligent highway and AV vehicle (AV) are considered to be the most effective ways to solve these problems. However, the dynamic uncertainty of driving environment factors is one of the key elements affecting vehicle driving safety, especially for AV, as well as traffic efficiency. The AV field has achieved fruitful results for this problem, but most of them focus on the identification of vehicle dynamics and visualization of roadside facilities. However, the feasibility and applicability of AV on the expressway system have not been tested in China. This paper summarized the development status and trend of AV and the difficulties and challenges of AV test on the expressway. Proposed test scenario of AV on the expressway, and on this basis, carried out a test and studied the adaptability of AV on the expressway.

The flash boiling phenomenon occurs at some operating conditions when fuel is directly injected into the cylinder of a homogeneous charge spark ignition direct injection (SIDI) engine due to the higher temperature of the injected fuel and lower back pressure. A flash boiling spray has significantly different characteristics from a conventional DI gasoline spray. In this paper, the planar laser-induced exciplex fluorescence (PLIEF) technique with two specially designed dopants of the fluorobenzene (FB) and the diethyl-methyl-amine (DEMA) in n-hexane was implemented to investigate the liquid and vapor phases of sprays from a multi-hole injector. A vapor phase calibration was carried out to quantitatively correlate the fluorescence signal with vapor concentration. The quantitative vapor concentration distribution is then obtained by applying the calibration.

In order to measure the droplets and vapor concentration inside a fuel spray, a dual-wavelength laser absorption-scattering technique was developed using the second harmonic (532nm) and the fourth harmonic (266nm) of a Nd:YAG laser and using dimethylnaphthalene as the test fuel. The investigation results show that dimethylnaphthalene, which has physical properties similar to diesel fuel, is almost transparent to visible light near 532nm and is a strong absorber of ultraviolet light near 266nm. Based on this result, the vapor concentration in a fuel spray can be determined by the two separate measurements: a transmission measurement at a non-absorbing wavelength to detect the droplets optical thickness and a transmission measurement at an absorbing wavelength to detect the joint vapor and droplets optical thickness. The droplets density can be determined by extinction imaging through the transmission at the non-absorbing wavelength.

In small and compact class vehicles equipped with diesel engines, the 2-valve-per-cylinder design still holds a significant share of the market. The current work describes the numerical simulation of port-valve-cylinder flow in a 1.2 liter 2-valve-per-cylinder diesel engine to characterize the performance of its manifold and intake ports. First, evaluation metrics were defined and analysis procedure was established for CFD assessment of intake manifold performance in multi-cylinder engines. Then the CFD analysis was carried out for the 2-valve engine in comparison with the baseline 4-valve reference engine. The results show that a complex interaction between intake port and flow distribution around TDC was found in the 2-valve engine, resulting in much higher mean flow velocity, inhomogeneity index/rotational momentum at the port inlet and consequently higher swirl ratio than the baseline 4-valve engine, which can cause high smoke at high load operations.

The interaction of fuel sprays with in-cylinder air flow is crucially important for the mixture preparation and subsequent combustion processes in gasoline direct injection (GDI) engines. In the present work, the experimentally validated computational fluid dynamics (CFD) simulations are performed to study the dynamics and physical insight of hollow-cone sprays interacting with a uniform crossflow. The basis of the model is the standard Reynolds-averaged Navier-Stokes (RANS) approach coupled to the Lagrangian treatment for statistical groups (parcels) representing the physical droplet population. The most physically suitable hybrid breakup models depicting the liquid sheet atomization and droplet breakup processes based on the linear instability analysis and Taylor analogy theory (LISA-TAB) are used. Detailed comparisons are made between the experiments and computations in terms of spray structure, local droplet diameter and velocity distributions.

In order to investigate effects of the multi-hole nozzle with micro orifices on mixture formation processes in Direct-Injection Diesel engines, mixture characteristics were examined via an ultraviolet-visible laser absorption scattering (LAS) technique under various injectors. The injection quantity per orifice per cycle was reduced by nozzle hole sizes. The LAS technique can provide the quantitative and simultaneous measurements of liquid and vapor phases concentration distributions inside of the fuel spray. Mass of ambient gas entrained into the spray, liquid/ vapor mass and mean equivalence ratio of total fuel were obtained based on Lambert Beer's law. As a result, the leaner and more homogeneous fuel-gas mixture can be achieved by reducing the nozzle hole diameter, in the meanwhile more ambient gas were entrained into the spray. Moreover, relationships between mixture formation and D.I.

The concept of two closely spaced micro-orifices (group hole nozzle) has been studied as a promising technology for the reduction of soot emission from direct injection (DI) diesel engines by improving the fuel atomization and evaporation. One of the main issues on group hole nozzle is the arrangement of orifices with various distances and angles. In this study, the ignition and combustion characteristics of wall-impinging diesel sprays from group-hole nozzles were investigated with various angles between two micro-orifices (included angles). A laser absorption scattering (LAS) technique for non-axisymmetric sprays, developed based on a LAS technique for axisymmetric spray, was applied to investigate the liquid/vapor mass distribution of wall-impinging sprays. The direct flame images and OH radical images inside a high pressure constant volume vessel were captured to analyze the effect of included angle on spray ignition and combustion characteristics.

The group-hole (GH) nozzle concept that uses two closely spaced micro-orifices to substitute the conventional single orifice has the potential to facilitate better fuel atomization and evaporation, consequently attenuate the soot emission formed in direct-injection (D.I.) diesel engines. Studies of quantitative mixture properties of the transient fuel spray injected by the group-hole nozzles were conducted in a constant volume chamber via the laser absorption-scattering (LAS) technique, in comparison with conventional single-hole nozzles. Specific areas investigated involved: the non-evaporating and the evaporating ambient conditions, the free spray and the spray impinging on a flat wall conditions. The particular emphasis was on the effect of one of key parameters, the interval between orifices, of the group-hole (SH) nozzle structure.

Spray atomization and evaporation are expected to be improved by injecting fuel at a superheated state. However, the breakup mechanism and evaporation processes of superheated sprays have not been clarified. In previous studies [1], the multi-hole spray flow-field on the vertical plane through the spray axis was investigated by using high-speed particle image velocimetry (PIV). The results showed that the spray plumes collapse to the spray axis under high superheat conditions. It's also proven that the superheat degree is the predominant factor influencing the structure and the flow-field of the spray. To further understand this process, the interaction among spray plumes on three cross-sectional planes under various superheated conditions is investigated. In this study, n-hexane sprays generated from an eight-hole DI injector were measured using a high-speed PIV system. The results provide insight to the spray-collapse processes and the interaction between the spray plumes.

Superheated spray is expected to improve the fuel atomization and evaporation processes by introducing fuel temperature as a new control parameter in spark-ignited direct-injection (SIDI) engines. In this study, flow fields of n-hexane spray from a multi-hole injector in both vertical and cross-sectional directions were investigated by using high-speed particle image velocimetry (HS-PIV) within the lower density regions. The results provide insight to the spray-collapsing processes under various superheated conditions. It was found that in axial direction, the vertical velocity increases while the radial velocity decreases with increasing superheat degree, which determines the convergent spray structure. In cross-sectional direction, the dynamic variation of the spray structure and interaction among spray plumes were investigated. The relationship between the spray structure and flow field was found. The flow patterns during and after the injection are significantly different.

When heated fuel is injected into an ambient environment below its saturation pressure, the fuel could reach superheated state and experience flash boiling. Comparing with the non-flash boiling spray, namely the single phase liquid spray, flash boiling spray is characterized by its nature of two phase flow, due to vapor bubbles constantly generating inside the liquid phase. The behavior of those microscopic scale bubbles could introduce prompt spray atomization and vaporization, resulting in dramatically different spray characteristics. Comparing with the sprays generated via a high pressure injection system, the flash boiling spray has much shorter penetration, wider spray angle, more uniformly distributed mass, quicker evaporation, and smaller drop sizes, etc., which are ideal for the direct-injection (DI) gasoline and diesel engine applications without the hassle and the high cost associated with the high pressure injection system.

As the vehicle emission regulations become stricter worldwide, one way to meet the emission requirements is to engage the use of alternative fuels in engine combustion. In this investigation, the early combustion processes of regular gasoline and alternative fuels, including ethanol and butanol, were studied by simultaneously recording both the in-cylinder pressure and the crank angle-resolved high-speed flame images in a single-cylinder spark-ignition direct-injection engine. The engine was equipped with a quartz insert in the piston which provided an optical access to its cylinder through the piston. The effects of engine coolant & oil temperatures and intake air swirl ratio on the early flame development were also studied. The heat release was derived from the in-cylinder pressure measurements and the corresponding flame area characteristics were extracted from the images.

The previous study indicates that the detonation waves generated by acetylene/oxygen mixture can converge in the combustion chamber. In order to verify the destructive effect of detonation wave convergence on piston materials, the detonation bomb device was modified to fundamentally investigate the material failures of aluminum alloy for pistons. The results show that the specimens are destroyed in the middle and edge region after dozens of detonations, which is consistent with the typical characteristics of the piston failures in engines. Therefore, the hypothesis that failures of piston material is caused by the detonation wave convergence is verified.

The group-hole nozzle concept is regarded as a promising approach to facilitate better fuel atomization and evaporation for direct injection diesel engine applications. In the present work, the spray and mixture properties of group-hole nozzle with close, parallel or a small included angle orifices were investigated experimentally by means of the ultraviolet-visible laser absorption-scattering (LAS) imaging technique, in comparison with the conventional single-hole nozzle. Three series of group-hole nozzles were designed to investigate the effect of group-hole nozzle specification while varying the included angle and interval between the orifices. The results suggested that: 1) Group-hole nozzle with very close, parallel orifices presents the similar spray characteristics with those of the single-hole nozzle.

While the use of injection strategies utilizing multiple injection events for each engine cycle has become common, there are relatively few studies of the spray structure of split injection events. Optical spray measurements are particularly difficult for split injection events with a short dwell time between injections, since droplets from the first injection will obscure the end of the first and the start of the second injection. The current study uses x-ray radiography to examine the near-nozzle spray structure of split injection events with a short dwell time between the injection events. In addition, x-ray phase-enhanced imaging is used to measure the injector needle lift vs. time for split injections with various dwell timings. Near the minimum dwell time needed to create two separate injection events, the spray behavior is quite sensitive to the dwell time.

It is well know that the internal flow field and nozzle geometry affected the spray behavior, but without high-speed microscopic visualization, it is difficult to characterize the spray structure in details. Single-hole diesel injectors have been used in fundamental spray research, while most direct-injection engines use multi-hole nozzle to tailor to the combustion chamber geometry. Recent engine trends also use smaller orifice and higher injection pressure. This paper discussed the quasi-steady near-nozzle diesel spray structures of an axisymmetric single-hole nozzle and a symmetric two-hole nozzle configuration, with a nominal nozzle size of 130 μm, and an attempt to correlate the observed structure to the internal flow structure using computational fluid dynamic (CFD) simulation. The test conditions include variation of injection pressure from 30 to 100 MPa, using both diesel and biodiesel fuels, under atmospheric condition.

Experimental results of a diesel engine have shown that using split-injection can reduce the NOx and particulate emissions. For understanding the mechanism of emissions reduction, mixture formation in split-injection diesel sprays was characterized in the present paper. A dual-wavelength laser absorption-scattering (LAS) technique was developed by use of the second harmonic (532nm) and the fourth harmonic (266nm) of a pulsed Nd:YAG laser as the incident light and dimethylnaphthalene (DMN) as the test fuel. By applying this technique, imaging was made of DMN sprays injected into a high-temperature and high-pressure constant volume vessel by a single-hole nozzle incorporated in a common rail injection system for D.I. diesel engine. The line-of-sight optical thickness of both fuel vapor and droplets in the sprays was yielded from the sprays images.

Mixture formation processes play a vital role on the performance of a D.I. Gasoline engine. Quantitative measurement of liquid and vapor phase concentration distribution in a D.I. gasoline spray is very important in understanding the mixture formation processes. In this paper, an unique laser absorption scattering (LAS) technique was employed to investigate the mixture formation processes of a fuel spray injected by a D.I. gasoline injector into a high pressure and temperature constant volume vessel. P-xylene, which is quite suitable for the application of the LAS technique, was selected as the test fuel. The temporal variations of the concentration distribution of both the liquid and vapor phases in the spray were quantitatively clarified. Then the effects of injection pressure and quantity on the concentration distributions of both the liquid and vapor phases in the spray were analyzed.