David L. S. Hung

A practical guide for using proper orthogonal decomposition in engine research

Proper orthogonal decomposition has been utilized for well over a decade to study turbulence and cyclic variation of flow and combustion properties in internal combustion engines. In addition, proper orthogonal decomposition is useful to quantitatively compare multi-cycle in-cylinder measurements with numerical simulations (large-eddy simulations). However, the application can be daunting, and physical interpretation of proper orthogonal decomposition can be ambiguous. In this paper, the mathematical procedure of proper orthogonal decomposition is described conceptually, and a compact MATLAB® code is provided. However, the major purpose is to empirically illustrate the properties of the proper orthogonal decomposition analysis and to propose practical procedures for application to internal combustion engine flows. Two measured velocity data sets from a motored internal combustion engine are employed, one a highly directed flow (each cycle resembles the ensemble average), and the other an undirected flow (no cycle resembles the average). These data are used to illustrate the degree to which proper orthogonal decomposition can quantitatively distinguish between internal combustion engine flows with these two extreme flow properties. In each flow, proper orthogonal decomposition mode 1 is an excellent estimate of ensemble average, and this study illustrates how it is thus possible to unambiguously quantify the cyclic variability of Reynolds-averaged Navier–Stokes ensemble average and turbulence. In addition, this study demonstrates the benefits of comparing two different samples of cycles using a common proper orthogonal decomposition mode set derived by combining the two samples, the effect of spatial resolution, and a method to evaluate the number of snapshots required to achieve convergence.

Gasoline Fuel Injector Spray Measurement and Characterization – A New SAE J2715 Recommended Practice

With increasingly stringent emissions regulations and concurrent requirements for enhanced engine thermal efficiency, a comprehensive characterization of the automotive gasoline fuel spray has become essential. The acquisition of accurate and repeatable spray data is even more critical when a combustion strategy such as gasoline direct injection is to be utilized. Without industry-wide standardization of testing procedures, large variablilities have been experienced in attempts to verify the claimed spray performance values for the Sauter mean diameter, Dv90, tip penetration and cone angle of many types of fuel sprays. A new SAE Recommended Practice document, J2715, has been developed by the SAE Gasoline Fuel Injection Standards Committee (GFISC) and is now available for the measurement and characterization of the fuel sprays from both gasoline direct injection and port fuel injection injectors. A primary motivation for the development of the standardized procedures for test configuration, data acquisition, data reduction and reporting was to achieve significant reductions in the test-to-test and laboratory-to-laboratory variabilities of such reported spray data. All of the major areas of fuel injector spray testing and characterization are addressed in detail in the document, including spray imaging, high-resolution patternation and drop sizing by both phase-Doppler interferometry and laser diffraction. Valuable lessons regarding the definitions and interpretations of commonly-used spray parameters were learned during the development of the J2715 document, and these are presented and discussed. Based upon the five years of committee discussions and consensus decisions, five key recommendations on fuel spray measurement and characterization are made to the worldwide automotive industry. The first, and most important, recommendation is that the Recommended Practices in SAE J2715 be utilized by the spray laboratories of all automotive companies and injector 2008-01-1068 Gasoline Fuel Injector Spray Measurement and Characterization – A New SAE J2715 Recommended Practice

Modeling and Inverse Compensation of Temperature-Dependent Ionic Polymer–Metal Composite Sensor Dynamics

Ionic polymer-metal composites (IPMCs) have intrinsic sensing capabilities. Like many other sensing materials, however, IPMC sensors demonstrate strong temperature-dependent behaviors. In this paper, we present the first systematic studies on temperature-dependent IPMC sensing dynamics. A cantilevered IPMC beam, soaked in a water bath with controlled temperature, is excited mechanically at its tip. The empirical frequency response of the sensor, with the tip displacement as an input and the short-circuit current as an output, shows a clear dependence on the bath temperature. The sensing dynamics is modeled with a transfer function with temperature-dependent coefficients. By fitting the values of the coefficients at a set of test temperatures, we capture the temperature dependence of the coefficients with polynomial functions, which can be used to predict the sensing dynamics at other temperatures. We also investigate the inversion of the sensing dynamics, for extracting the mechanical signal given the sensor output. A stable but noncausal inversion algorithm is applied to deal with the unstable zeros of the original sensing dynamics. Inversion with finite preview time is further explored to achieve near real-time decoding of the sensor output. Experimental results with both harmonic stimuli and free vibrations have validated the effectiveness of the proposed modeling and inversion schemes for IPMC sensors under different temperatures.

Model-Based Estimation of Flow Characteristics Using an Ionic Polymer–Metal Composite Beam

An ionic polymer-metal composite (IPMC) beam is capable of producing an electric signal closely correlated with its mechanical movement, due to the redistribution of mobile ions inside the IPMC material. Motivated by the potential application of this intrinsic sensing characteristic to flow property measurements in automotive engines, this paper investigates the feasibility of detecting the start and end of a pulsating flow and its fluid characteristics using an IPMC-beam-based sensor. A dynamic model is developed for the IPMC beam under the flow. The model consists of multiple rigid elements connected by rotational springs and, under suitable conditions, has a closed-form solution that enables efficient estimation of fluid properties and flow parameters with the least-squares minimization approach. The proposed fluid estimation scheme is validated using experimental results with different fluid media, and it is found that the estimated fluid drag coefficients (highly correlated with fluid viscosity) have good agreement with their actual values. This is very important for automotive applications where the characteristics of the fuel blend (such as gasoline and ethanol) need to be identified in real time.

A High Speed Flow Visualization Study of Fuel Spray Pattern Effect on Mixture Formation in a Low Pressure Direct Injection Gasoline Engine

In developing a direct injection gasoline engine, the incylinder fuel air mixing is key to good performance and emissions. High speed visualization in an optically accessible single cylinder engine for direct injection gasoline engine applications is an effective tool to reveal the fuel spray pattern effect on mixture formation The fuel injectors in this study employ the unique multi-hole turbulence nozzles in a PFI-like (Port Fuel Injection) fuel system architecture specifically developed as a Low Pressure Direct Injection (LPDI) fuel injection system. In this study, three injector sprays with a narrow 40° spray angle, a 60°spray angle with 5°offset angle, and a wide 80° spray angle with 10° offset angle were evaluated. Image processing algorithms were developed to analyze the nature of in-cylinder fuel-air mixing and the extent of fuel spray impingement on the cylinder wall. Test data reveal that for a given cylinder head, piston configuration and intake air port flow characteristics, injector spray pattern plays a dominating role in how the fuel-air mixture is formed. If an appropriate injector spray pattern is chosen, the in-cylinder fuel mixing can be enhanced by minimizing fuel impingement on cylinder wall, piston top, and intake valves, thus producing a more homogeneous fuel-air mixture prior to the ignition. Engine designers can select a specific spray pattern to improve the fuel-air mixture optimized for specific parameters such as engine head, piston, valve configuration, intake air flow characteristics, fuel injection strategy, injector mounting and operating conditions.

Combustion Characteristics of a Single-Cylinder Engine Equipped with Gasoline and Ethanol Dual-Fuel Systems

The requirement of reduced emissions and improved fuel economy led the introduction of direct-injection (DI) spark-ignited (SI) engines. Dual-fuel injection system (direct-injection and port-fuel-injection (PFI)) was also used to improve engine performance at high load and speed. Ethanol is one of the several alternative transportation fuels considered for replacing fossil fuels such as gasoline and diesel. Ethanol offers high octane quality but with lower energy density than fossil fuels. This paper presents the combustion characteristics of a single cylinder dual-fuel injection SI engine with the following fueling cases: a) gasoline for PFI and DI, b) PFI gasoline and DI ethanol, and c) PFI ethanol and DI gasoline. For this study, the DI fueling portion varied from 0 to 100 percentage of the total fueling over different engine operational conditions while the engine air-to-fuel ratio remained at a constant level. It was shown in all cases that the IMEP (indicated mean effective pressure) decreases by as much as 11% as DI fueling percentage increases, except in case b) where the IMEP increases by 2% at light load. The combustion burn duration increases significantly at light load as DI fueling percentage increases, but only moderately at WOT (wide open throttle). In addition, the percentage of the ethanol in the total fueling plays a dominant role in affecting the combustion characteristics at light load; but at heavy load (WOT), the DI fueling percentage becomes an important parameter, regardless of the percentage of ethanol content in the fuel.

Combustion characteristics of a single-cylinder spark ignition gasoline and ethanol dual-fuelled engine

Abstract The requirements of reduced emissions and improved fuel economy led to the introduction of direct-injection (DI) spark ignition (SI) engines. A dual-fuel injection system (DI and port fuel injection (PFI)) was also used to improve engine performance at high-speed high-load conditions. Ethanol is one of the several alternative transportation fuels considered for replacing fossil fuels such as gasoline and diesel. Ethanol offers high octane quality but with lower energy density than fossil fuels. This paper presents the combustion characteristics of a single-cylinder dual-fuel injection SI engine with the following fuelling cases: case A, gasoline for both PFI and DI; case B, gasoline PFI and ethanol DI; case C, ethanol PFI and gasoline DI. For this study, the DI fuelling portion varied from 0 per cent to 100 per cent of the total fuelling over different engine operational conditions while the engine air-to-fuel ratio remained at a constant level. It was shown in all cases that the indicated mean effective pressure (IMEP) decreases by as much as 11 per cent as the DI fuelling percentage increases, except in case B where the IMEP increases by 2 per cent at a light load. The combustion burn duration increases significantly at a light load as the DI fuelling percentage increases, but only moderately at wide-open throttle (WOT). In addition, the percentage of the ethanol in the total fuelling plays a dominant role in affecting the combustion characteristics at a light load but, at a heavy load (WOT), the DI fuelling percentage becomes an important parameter, regardless of the percentage of ethanol content in the fuel.

Simultaneous two-phase flow measurement of spray mixing process by means of high-speed two-color PIV

In this article, a novel high-speed two-color PIV optical diagnostic technique has been developed and applied to simultaneously measure the velocity flow-fields of a multi-hole spark-ignition direct injection (SIDI) fuel injector spray and its ambient gas in a high-pressure constant volume chamber. To allow for the phase discrimination between the fuel droplets and ambient gas, a special tracer-filter system was designed. Fluorescent seeding particles with Sauter mean diameter (SMD) of 4.8 µm were used to trace the gas inside the chamber. With a single high-speed Nd:YLF laser sheet (527 nm) as the incident light source, the Mie-scattering signal marked the phase of the fuel spray, while the fluorescent signal generated from the seeding particles tracked the phase of ambient gas. A high-speed camera, with an image-doubler (mounted in front of the camera lens) that divided the camera pixels into two parts focusing on the same field of view, was used to collect the Mie-scattering signal and LIF (laser induced fluorescence) signal simultaneously with two carefully selected optical filters. To accommodate the large dynamic range of velocities in the two phases (1–2 orders of magnitude difference), two separation times (dt) were introduced. This technique was successfully applied to the liquid spray and ambient gas two-phase flow measurement. The measurement accuracy was compared with those from LDV (laser Doppler velocimetry) measurement and good agreement was obtained. Ambient gas motion surrounding the fuel spray was investigated and characterized into three zones. The momentum transfer process between the fuel spray and ambient gas in each zone was analyzed. The two-phase flow interaction under various superheated conditions was investigated. A strengthened momentum transfer from the liquid spray to the ambient was observed with increased superheat degree.

A study of fuel impingement analysis on in-cylinder surfaces in a direct-injection spark-ignition engine with gasoline and ethanol-gasoline blended fuels

An experimental study is performed to investigate the fuel impingement on cylinder walls and piston top inside a directinjection spark-ignition engine with optical access to the cylinder. Three different fuels, namely, E85, E50 and gasoline are used in this work. E85 represents a blend of 85 percent ethanol and 15 percent gasoline by volume. Experiments are performed at different load conditions with the engine speeds of 1500 and 2000 rpm. Two types of fuel injectors are used; (i) High-pressure production injector with fuel pressures of 5 and 10 MPa, and (ii) Low-pressure production-intent injector with fuel pressure of 3 MPa. In addition, the effects of split injection are also presented and compared with the similar cases of single injection by maintaining the same amount of fuel for the stoichiometric condition. Novel image processing algorithms are developed to analyze the fuel impingement quantitatively on cylinder walls and piston top inside the engine cylinder. Qualitative details of spray tip penetration are also presented to reveal the effects of ethanol fuels compared to that of gasoline. It is found that the split injection is an effective way to reduce the overall fuel impingement on in-cylinder surfaces. No significant difference is observed on fuel spray pattern when gasoline is compared with E50 and E85. However, spray tip penetration is slightly higher with gasoline than that of ethanol fuels. Results also show that the wall impingement is higher with gasoline compared to ethanol fuels. INTRODUCTION Improvement in fuel efficiency and reduction in exhaust emissions are the main goals behind the new developments in internal combustion (IC) engines. The concept of directinjection spark-ignition (DISI) engine has the potential to achieve such goals. In this technology, fuel is directly injected into the engine cylinder, which offers great flexibility to control the fuel injection timing, its duration and the number of injections. Note that the fuel-air mixture preparation in the combustion chamber is one of the key factors that influences the in-cylinder combustion characteristics and hence the engine performance (Hung et al., 2007). Therefore, optimizing the fuel-air mixture homogeneity is an important parameter for the engine designers. In general, a homogeneous fuel-air mixture is achieved by injecting the fuel during the intake stroke. However, due to in-cylinder injection and higher injection pressures, the fuel impingement levels on in-cylinder surfaces in DISI engines are typically higher than those in port-fuel injection (PFI) engines (Pereira et al., 2007). This results in an increase in the levels of un-burned hydrocarbons and smoke emissions, which reduces the potential fuel economy benefits associated with the direct-injection engines. Therefore, it is important to control the fuel injection timing precisely in order to minimize the fuel impingement on incylinder surfaces. Several studies have been reported on fuel spray pattern visualization and its influence on mixture formation inside the cylinder of direct-injection systems. Grimaldi et al. (2000) A Study of Fuel Impingement Analysis on InCylinder Surfaces in a Direct-Injection SparkIgnition Engine with Gasoline and Ethanol-Gasoline Blended Fuels 2010-01-2153 Published 10/25/2010

Characteristics of Flash Boiling Fuel Sprays from Three Types of Injector for Spark Ignition Direct Injection (SIDI) Engines

Spark ignition direct injection (SIDI) gasoline engines employ high fuel injection pressure to promote the liquid fuel atomization and vaporization in the combustion chamber. However, high fuel injection pressures normally lead the fuel spray over penetrating in engine cylinder, resulting in wall and/or piston wetting which cause high level of engine unburned hydrocarbon (UHC) and soot emissions. Recently, it has been found the fuel temperature could play important roles in spray atomization and vaporization processes. Especially, when the temperature of the fuel exceeds its local boiling point, the fuel is superheated and flash boiling occurs. Experiments of flash boiling sprays from a multi-hole DI injector show that the spray would undergo significant structural transformation under the superheated conditions. Both the atomization and vaporization are improved when the phenomenon of flash boiling occurs. Meanwhile, since various types of SIDI engine combustion systems utilize different fuel injector configurations to achieve desirable mixture formation and combustion, it is necessary to extend the existing knowledge of flash boiling spray from multi-hole injector to other types of injector, and characterize their flash boiling spray behaviour under the similar superheated conditions. In this paper, flash boiling sprays from three types of SIDI injectors, namely, multi-hole, swirl and outward opening injectors are investigated at a high pressure constant volume chamber. The primary focus is the spray from a multi-hole injector as it is most widely used in modern SIDI engines. The temperature of the injector body can be regulated by placing the injector in a fixture which can be thermally controlled. Various laser diagnostics are applied to investigate the spray geometry, flow field, vaporization and droplet size distributions. The results show that the characteristics of flash boiling spray are mainly dominated by superheat degree, i.e., the difference between the fuel temperature and its boiling point, not as sensitive to the injection pressure as the non-flash boiling spray. The structures of flash boiling spray from all three types of injector differ from those of non-flash boiling spray significantly. However, the effects of injector configuration on the structure of flash boiling spray are insignificant, compared to the non-flash boiling sprays. This study reveals that using fuel temperature can be an effective parameter for controlling the spray structure, spray atomization and evaporation.