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

Abstract

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.

Fuel spray visualization and its impingement analysis on in-cylinder surfaces in a direct-injection spark-ignition engine

“…It has been shown previously (Hung et al 2007) that multi-hole fuel injectors offer flexible spray pattern which can be tailored for a specific cylinder configuration. As fuel is injected directly into the engine cylinder, spray may mix well with the intake air or impinge on the in-cylinder surfaces such as piston top and cylinder wall.…”

“…The dimensions and their physical constraints of the engine cylinder head only allows the injector to be placed on the top side at about 12°along the piston axis in the vicinity of the spark plug (i.e., a centrally mounted injector configuration). Two types of multi-hole fuel injectors are considered; (i) low-pressure direct-injection (LPDI) 9-hole fuel injector with the fuel pressure of 3 MPa (Hung et al 2007) and (ii) highpressure direct-injection (HPDI) 7-hole fuel injector with the fuel pressures of 5 and 10 MPa. The advantage of the multi-hole injector is that the hole pattern, hole orientation, internal flow cavity, and number of holes of a nozzle can all be designed to control individual spray plumes and the overall spray pattern, providing enhanced droplet dispersion in the cylinder with reduced fuel impingement on cylinder walls.…”

“…They found that the main part of the hollow cone spray was influenced strongly by the air motion, although the influence of the air motion on the central part was weak. Hung et al (2007) used high-speed imaging to visualize the spray pattern in a single cylinder DISI engine. Three spray patterns, i.e., a narrow 40°spray angle, a 60°spray angle with 5°offset angle, and a wide 80°spray angle with 10°offset angle, were studied by the authors.…”

Characterization of the Inlet Port Flow under Steady-State Conditions Using PIV and POD

“…The main issue is to achieve these kinds of mixture modes with different in-cylinder flow structures under these operating conditions, which control the mixture formation. Many studies were carried out to solve these issues through the proper design of the combustion chamber, as well as the development of GDI spray systems and injector characteristics [7][8][9][10][11][12][13][14][15]. Another key approach was to make practical and effective use of the full potential of the characteristics of the in-cylinder flow field.…”

High-Speed Flow and Combustion Visualization to Study the Effects of Charge Motion Control on Fuel Spray Development and Combustion Inside a Direct-Injection Spark-Ignition Engine

“…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 influence 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.…”