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High exhaust gas recirculation (EGR) tolerance is always pursued not only for its advantages of the pumping loss reduction and fuel economy benefit, but also for stringent emission requirements by using conventional three-way catalytic converter (TWC) instead of costly NOx trap. How to keep fresh charge and EGR separated in the cylinder of a conventional four valve gasoline engine is a critical challenge. This work establishes advanced user subroutines and overall simulation strategies to model engine in-cylinder turbulent flow, temperature, pressure, and EGR concentration fields and to simulate EGR stratification process in a typical pent-roof gasoline engine cylinder during intake and compression strokes.

The energy management strategies (EMS) for hybrid electric vehicles (HEV) have a great impact on the fuel economy (FE). The Pontryagin's minimum principle (PMP) has been proved to be a viable control strategy for HEV. The optimal costate of the PMP control can be determined by the given information of the driving conditions. Since the full knowledge of future driving conditions is not available, this paper proposed a dynamic optimization method for PMP costate without the prediction of the driving cycle. It is known that the lower fuel consumption the method yields, the more efficiently the engine works. The selection of costate is designed to make the engine work in the high efficiency range. Compared with the rule-based control, the proposed method by the principle of Hamiltonian, can make engine working points have more opportunities locating in the middle of high efficiency range, instead of on the boundary of high efficiency range.

The proper formation of fuel-air mixture, which depends to a large extend on the complex in-cylinder air flow, is an important criterion to control the clean and reliable combustion process in spark-ignition direct-injection (SIDI) engines. The in-cylinder flow vorticity field presents highly transient complex characteristics, and the corresponding vorticity field also evolves in the entire engine cycle from intake to exhaust strokes. It is also widely recognized that the vorticity field plays a key role in the in-cylinder turbulent field because it influences the air-fuel mixing and flame development process. In this investigation, the in-cylinder vortex structure and vorticity field characteristics are analyzed using the phase-invariant proper orthogonal decomposition (POD) method.

The preparation of fuel-air mixture and its efficient, clean, and reliable combustion in spark-ignition direct-injection (SIDI) engines depend to a large extend on the complex in-cylinder air flow. It has been widely recognized that the ensemble-averaged flow field provides rather limited understanding of in-cylinder air motion due to the strong cycle-to-cycle variations. In this study, time-resolved particle image velocimetry (PIV) is utilized to measure the in-cylinder air motion in a motored single-cylinder optical engine. Then, the velocity fields from different phases (crank-angle positions during intake and compression strokes) of 200 engine cycles are analyzed using phase-invariant proper orthogonal decomposition (POD) technique. With the phase-invariant POD method, the velocity fields from different phases are decomposed into a single set of POD modes. In this manner, the POD modes can be used to represent any phase of the flow.

It has been found that the spray impingement on piston for SIDI engines significantly influences engine emission and combustion efficiency. Fuel film sticking on the wall will dramatically cause deterioration of engine friction performance, incomplete combustion, and substantial cycle-to-cycle variations. When increasing the injection pressure, these effects are more pronounce. Besides, the ambient pressure also plays an important role on the spray structure and influences the footprint of impinging spray on the plate. However, the dynamic behavior of impinging spray and corresponding film was not investigated thoroughly in previous literature. In this study, simultaneous measurements of macroscopic structure (side view) and its corresponding footprint (bottom view) of impinging spray was conducted using a single-hole, prototype injector in a constant volume chamber.

A laser sheet imaging system with Mie-scattering and Laser Induced Fluorescence (LIF) was used to investigate the spray characteristics of gasoline, methanol and ethanol fuels. A range of conditions found in today's gasoline engines were investigated including that observed during engine cold-start. Both a swirl injector and a multi-hole fuel injector were examined for each of the three fuels. A combination of the second harmonic (532 nm) and the fourth harmonic (266 nm) was generated simultaneously using a Nd:YAG laser system to illuminate the spray. The Mie-scattering technique was used to characterize the liquid phase of the spray while the LIF technique was used to detect a combination of liquid and vapor phases. While gasoline naturally fluoresced, the dopant TEA was added to the methanol and ethanol fuels as a fuel tracer. The Mie-scattering and LIF signals were captured simultaneously using a CCD camera along with an image doubler.

To alleviate the shortage of petroleum resources and the air pollution caused by the burning of fossil fuels, the development of renewable fuels has attracted widespread attention. Among the various renewable fuels, ethanol can be produced from biomass and does not require much modification when applied to practical engines, so it has been widely used. However, ethanol fuel has a higher heat of vaporization than gasoline, it is difficult to evaporate and atomize under cold start conditions. Besides, the catalyst has not reached the conversion temperature at this time, resulting in lower conversion efficiency. These factors all lead to higher pollutant emission levels in ethanol-gasoline blends. To solve the above problems, this research used visualization techniques to compare the effects of flash boiling and high-energy ignition technologies on the in-cylinder combustion process and pollutant emission of ethanol-gasoline blends fuel.

The cycle-to-cycle variations of in-cylinder flow field represent a significant challenge which influence the stability, fuel economy, and emissions of engine performance. In this experimental investigation, the high-speed time-resolved particle image velocimetry (PIV) is applied to reveal the flow field variations of a specific swirl plane in a spark-ignition direct-injection engine running under two different swirl air flow conditions. The swirl flow is created by controlling the opening of a control valve mounted in one of the two intake ports. The objective is to quantify the cycle-to-cycle variation of in-cylinder flow field at different crank angles of the engine cycle. Four zones along the measured swirl plane are divided according to the positions of four valves in the cylinder head. The relevance index is used to evaluate the cycle-to-cycle variation of the velocity flow field for each zone.

Strong cycle-to-cycle variations of fuel spray are observed due to the highly transient in-cylinder airflow in spark-ignition direct-injection (SIDI) engine. The spray structure comparison based on ensemble-averaged image may be misleading sometimes because the spray images for the same engine running condition could be different from cycle to cycle. Also, the visual comparison of spray images from many cycles is only qualitative and very time-consuming. Therefore, the present paper provides a novel approach to make quantitative comparison of spray structures from different engine conditions, or comparison between experiment and simulation (such as large eddy simulation, LES). The methodology is based on the proper orthogonal decomposition (POD), which has been utilized for in-cylinder turbulent flow research for over a decade.

High fuel injection pressure has been regarded as a key controlling factor for internal combustion engines to achieve good combustion performance with reduced emissions and improved fuel efficiency. For common-rail injection system (CRS) used in advanced diesel engines, fuel injection pressure can often be raised to beyond 200 MPa. Although characteristics of diesel spray has been thoroughly studied, little work has been done at ultra-high injection pressures. In this work, the characteristics of CRS diesel spray under ultra-high injection pressure up to 250 MPa was investigated. The experiments were conducted in an optically accessible high-pressure and high-temperature constant volume chamber. The injection pressure varied from 50 MPa to up to 250 MPa. Both non-evaporating condition and evaporating condition were studied. A single-hole injector was specially designed for this investigation.

Increasing the injection pressure in DISI engine is an efficient way to obtain finer droplets but it will also potentially cause spray impingement on the cylinder wall and piston. Consequently, the fuel film sticking on the wall can dramatically increase the soot emission of the engine especially in a cold start condition. On the other hand, ethanol is widely used as an alternative fuel in DI engine due to its sustainable nature and high octane number. In this study, the fuel film characteristics of single-plume ethanol impinging spray was investigated. The experiments were performed under ultra-low fuel/plate temperature to simulate the cold start condition in cold areas. A low temperature thermostatic bath combined with specially designed heat exchangers were used to achieve ultra-low temperature for both the impinging plate and the fuel. Laser induced fluorescence (LIF) technique was employed to measure the thickness of fuel film deposited on the impinging plate.

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.

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.

It is well known that engine downsizing is still the main energy-saving technology for spark-ignition direct-injection (SIDI) engine. However, with the continuous increase of the boosting ratio, the gasoline engine is often accompanied by the occurrence of knocking, which has the drawback to run the engine at retarded combustion phasing. Besides, in order to protect the turbine blades from being sintered by high exhaust temperature, the strategies of fuel enrichment are often taken to reduce the combustion temperature, which ultimately leads to a high level of particulate number emission. Therefore, to address the issues discussed above, the port water injection (PWI) techniques on a 1.2-L turbocharged, three-cylinder, SIDI engine were investigated. Measurements indicate that the optimization of spark timing has a significant impact on its performance.

Homogeneous lean combustion is expected to be a key technology to further improve the combustion and reduce emissions of spark-ignition direct-injection engines. The application of lean combustion is facing many challenges such as slow flame propagation and combustion fluctuations. Under severe operating conditions such as low-speed lean-burn conditions, the weak in-cylinder airflow worsens the fuel and air mixing yielding difficulties in stable flame kernel initiation and consequently deteriorating flame propagation. In this study, the effect of flash boiling spray on flame kernel generation, flame propagation, engine performance, and exhaust emissions of the spark ignition direct injection (SIDI) engine under homogenous lean-burn conditions are investigated. A single-cylinder four-stroke optical SIDI engine was used in this study. The in-cylinder flash boiling and subcooled sprays during engine operation were compared using the Mie scattering technique.

High-dilution stratified EGR combustion system operating at stoichiometric air-fuel ratio (A/F) could offer significant fuel economy saving comparable to the lean burn or stratified charge direct injection SI engines, while still complies with stringent emission standards by using the conventional three-way catalytic converter. The most critical challenge is to keep substantial separation between EGR gas and air-fuel mixture, or to minimize the mixing between these two zones to an acceptable level for stable and complete combustion. Swirl-type stratified EGR and air-fuel flow structure is considered desirable for this purpose, because the circular engine cylinder tends to preserve the swirl motion and the axial piston movement has minimal effect on the flow structure swirling about the same axis. In this study, KIVA3V was used to simulate mixing and combustion processes in a typical pent-roof gasoline engine cylinder during compression and expansion strokes.

Spark-ignition direct-injection (SIDI) gasoline engine, especially in downsized boosted engine platform, has proven to be one of the most promising concepts to improve vehicle fuel economy. SIDI engines are also getting a larger share of the gasoline engine market which is traditionally dominated by the port fuel injection (PFI) engines in the U.S., European and Chinese vehicles. However, higher particle number emissions associated with operating the engine at higher loads pose additional challenges for meeting future stringent emissions regulations. In this study, the potential of using multiple injection strategies (double injection and triple injection strategy during the intake stroke in homogeneous combustion mode) to reduce particle number emissions in a 2.0 liter boosted SIDI gasoline engine at 1000 rpm, 11 bar BMEP condition was investigated using Horiba MEXA SPCS1000 PN measurement instrument.

Comparing with port-fuel-injection (PFI) engine, the fuel sprays in spark-ignition direct-injection (SIDI) engines play more important roles since they significantly influence the combustion stability, engine efficiency as well as emission formations. In order to design higher efficiency and cleaner engines, further research is needed to understand and optimize the fuel spray atomization and vaporization. This paper investigates the atomization and evaporation of n-pentane, gasoline and surrogate fuels sprays under realistic SIDI engine conditions. An optical diagnostic technique combining high-speed Mie scattering and Schlieren imaging has been applied to study the characteristics of liquid and vapor phases inside a constant volume chamber under various operating conditions. The effects of ambient temperature, fuel temperature, and fuel type on spray atomization and vaporization are analyzed by quantitative comparisons of spray characteristics.