Development-of-Gasoline-Direct-Injection-Engine.docx

New Development of Gasoline Direct Injection Engine in AsiaNew Development of Gasoline Direct Injection Engine Abstract: In recent years, as emission regulations being stricter, many automobile manufacturers and research institutions are both seeking ways to improve engine performance by injecting fuel into cylinder directly. This article gives an outline of development of GDI engine in Asia and emphatically introduces the Toyota GDI engine and Hyundai Theta II GDI engine.Keywords: GDI; Asia; Toyota; D-4S combustion system; Hyundai.6INTRODUCTIONThe requirement of reduced emissions is critical for modern automobiles. As a possible solution to increase the fuel economy and reduce emissions of automotive engines, GDI engines have been considered for many years. Compared with conventional PFI engines, GDI engines are higher full-load performance, lower emissions such as HC, NOx and CO emissions and better fuel economy. So far, several automobile manufacturers have introduced GDI engines to the worldwide markets. DEVELOPMENTMitsubishi was the first to develop gasoline direct injection engine 4G93 1.8L inline-four in the market in 1996. It is available in both SOHC and DOHC versions. It also developed the first six-cylinder GDI engine, the 6G74 3.5L V6, in 1997. It had a crown-curved rather than flat combustion chamber, upright intake ports rather than angled, and a 10.4:1 compression ratio. Mitsubishi claimed 30 percent better fuel economy, a 30 percent reduction in emissions, and higher power outputs than diesels.Nissan released the Leopard featuring the VQ30DD equipped with direct injection in 1997. The engine has bore and stroke of 93mm and 73.3mm, with a compression ratio of 11:1. In 1998, the first direct injection system of Toyota D4 appeared on Japanese market vehicles equipped with the SZ and NZ engines. Toyota later introduced its D4 system to European markets with the 1AZ-FSE engine found in the 2001 Avensis. In 2005, Lexus GS 300 equipped with the 3GR-FSE engine was found in US markets. Toyotas 2GR-FSE V6 uses a more advanced direct injection system, which combines both direct and indirect injection using two fuel injectors per cylinder, a traditional port fuel injector (low pressure) and a direct fuel injector (high-pressure) in a system known as D4-S. In 2003, Honda released its own direct injection system on the Stream sold in Japan. Hondas fuel injector is placed directly atop the cylinder at a 90-degree angle rather than a slanted angle. In 2005, Mazda began to use their own version of direct-injection in the Mazdaspeed6 and later on the CX-7 sport-utility, and the new Mazdaspeed3 in the US and European market. It is referred to as Direct Injection Spark Ignition (DISI). In 2011, the Hyundai Sonata 2011 use GDI engines. Hyundais Theta I-4 engine family is a proprietary design, engineered in Namyang, Korea and currently in production for applications all over the world.TOYOTA 1st GENERATION GDI ENGINESThe Toyota first-generation direct-injection combustion system, the D-4 is swirl-based, wall-guided (Fig.1). Fig.1 Schematic of the Toyota first-generation D-4 engine systemThe helical intake port utilizes a variable-valve-timing-intelligent (VVT-i) cam-phasing system on the intake camshaft. According to engine operating conditions, valves can be controlled to acquired desired angle. The engine uses swirl current valve (SCV) in different load conditions. The SCV is closed in light-load condition to form a stratified air-fuel mixture. The SCV is opened in heavy-load to form homogeneous mixture.It is hard for fuel flow to penetrate against high environmental pressure and atomize in a short time during the compression stroke, so high fuel injection pressure is necessary. The newly developed high pressure swirl injector (Fig.2) uses an injection pressure of 12 MPa to meet these requirements. The direction of injection is offset from the spark plug to allow enough time for the fuel to vaporize.Fig.2 Swirl injectorThe D-4 engine also uses a NOx storage catalyst. The stored NOx is converted at time intervals of 50 seconds during lean operation by utilizing very brief periods of stoichiometric operation. TOYOTA 2nd GENERATION GDI ENGINESIn 1999, Toyota marketed a second-generation D-4 combustion system (Fig.3). This latest D-4 engine operates in three modes: (1) for cold start, high-load, or NOx-reduction operations is homogeneous-charge combustion with an air/fuel ratio in the range of 12:1 to 15:1;(2) for medium-load operation is weakly-stratified-charge combustion with an air/fuel ratio between 15:1 and 30:1; (3) for low-load operation is stratified-charge, lean-to-ultra-lean operation, employing an air/fuel ratio ranging from 17:1 to 50:1. Fig.3 Schematic of the Toyota first-generation D-4 engine systemCompared to the first-generation D-4 combustion system, one of the major changes is the elimination of the helical port, which enables the latest D-4 combustion system to achieve both excellent homogeneous-charge combustion and a wide range of stratified-charge combustion without relying on a variable-flow-control system (Fig.4). Fig.4 Combustion system configurationAnother advantage is achieving an extended range of stable stratified-charge combustion at both higher load and higher engine speed. It mainly owns to slit nozzle injectors with the stratified mixture guided by the pistons oval-shaped wall cavity. The slit nozzle injector generates a fan-shaped, 20offset spray enable the avoidance of an overly-rich mixture, even with an increased fuel quantity being delivered at higher loads (Fig.5). Fig.5 Slit nozzle and fan-shaped sprayA new V-6 3.0L engine (3GR-FSE) was introduced to the Japanese market at the end of 2003, and to the North American European markets, for the new Lexus GS300 at the beginning of 2005. This new V-6 employs the above-mentioned second generation stoichiometric D-4 system mainly to obtain high WOT performance and high thermal efficiency. Compared to conventional PFI engines, the power outputs can increase more than 10% and the reduction of fuel consumption can reach 30%. Except for employing stoichiometric direct injection, this engine also uses intake and exhaust variable valve timing (Dual VVT-i) systems, and reduces engine friction, to achieve a maximum power of 183kW at 6200rpm, and maximum torque of 312Nm at 3600rpm. Additionally the engine can met ULEV exhaust emission standards easily by using fast warm-up technology with stratified combustion. TOYOTA D-4S SYSTEMA new V-6 3.5L gasoline engine (2GR-FSE) uses a newly developed stoichiometric direct injection system D-4S (Direct injection 4-stroke gasoline engine system Superior version) with two fuel injectors in each cylinder. One is a direct injection injector generating a dual-fan-shaped spray with wide dispersion, while the other is a port injector. Fig. 6 shows the detail of D-4S system.Fig.6 A perspective view of D-4S combustion system chamberFor increasing air-flow at high engine speeds, the system utilizes high flow efficiency intake-ports and installs a PFI injector in the high flow efficiency intake-ports. The DI injectors has a dual-fan-shaped spray (Fig.7) injected vertically into the cylinder and spreads toward the exhaust side of the combustion chamber. This is why the spray has wide dispersion ability in the cylinder.Fig.7 Dual-fan-shaped spray shapeCFD analysis of the mixture distribution in the cylinder was conducted to reveal the effect of the newly developed spray. Star-CD was used as a solver and mesh generator for CFD analysis. Approximately 470,000 cells were made for these analyses. Fig. 8 shows the spray pattern injected into the cylinder. The dual-fan-shaped spray is injected perpendicularly to the piston and with wide dispersion in the cylinder. For this reason the spray is injected without being trapped by the piston cavity and the spray is injected without being trapped by the piston cavity and the combustion chamber. On the other hand, the conventional spray is trapped by the piston cavity and cannot spread toward the exhaust side of the combustion chamber. As a result the newly developed spray can make a homogeneous mixture in the cylinder. This spray can spread in the cylinder without intense in-cylinder air-motion. The conventional spray, alternatively, makes a less homogeneous mixture especially on the exhaust side of the combustion chamber. This lean region is because the spray itself does not have the ability to spread inside the cylinder. Fig.8 Comparison of the spray pattern calculated by CFDThe effect on emissions reduction with simultaneous injection was studied. Fig.9 shows the result of simultaneous injection from engine cranking to fast idling. In order to reduce the amount of fuel injected before the engine starts, PFI injection is utilized during engine cranking; compared to a conventional DISI engine, HC emissions is reduced about 20%. Furthermore, simultaneous injection is utilized during fast idling after the engine starts. Fig.9 Result of reduction of THC at fast idling with the simultaneous injectionOwning to Simultaneous injection, HC emissions can be reduced by approximately 20%. Simultaneous injection can suppress torque fluctuations so that the ignition timing can be retarded the same as a DI injection although the amount of fuel injected by the DI injector during the compression stroke is reduced. As a result, HC emissions can be reduced to the target level during the first 20 seconds of fast idling after the engine starts. For this reason this engine is potential to meet SULEV standards. HYUNDAI THETA II GDI ENGINEIn the 2011 Hyundai Sonata and Kia Optima are equipped with Theta II GDI engines. It features hollow stainless-steel DOHC with powder-metal cam lobes, continuously variable valve timing (CVVT) works on the intake side.When fuel pressure is reached above the specified pressure during cranking, fuel is injected into shallow bowl piston in the condition of higher air temperature during compression stroke. Less fuel is injected for the stable start. So, HC emission is minimized. After start, fuel is injected in intake and compression stroke, and spark timing is retarded for reducing catalyst heating time. The duration of emitting most of HC emission before catalyst heating is shortened and HC&NOx emissions are minimized. Unlike PFI engine, high pressure fuel in the GDI engine is injected during intake stroke or the piston going up during compression stroke. The wall film in cylinder is minimized for avoiding oil dilution, lowering smoke and maximizing the volumetric efficiency by cooling of intake air.Fig.10 shows the combustion system of 2.4L GDI engine. To avoid wall wetting of fuel injected into cylinder and minimize injector offset, the installation angle of injector is increased as big as possible. The position of injector tip is optimized by better cooling and less carbon deposit to avoid coking. Intake port is enlarged. Compared with base engine, flow capacity in intake port is increased by 4% for high performance.Fig.10 Combustion system of 2.4L GDI engineThe engine also optimizes combustion chamber. The position of spark plug tip is downwards and the radius of pent roof is increased for suppressing knock. Fig.11 show the cavity around injector tip that is shaped for avoiding the interference between spray and combustion chamber and minimizing carbon deposit around injector tip. Piston has the proper shallow bowl in top surface for stable combustion when compression starts and split injection catalyst heating without performance loss by side effect of bowl in operation of full load. Fig.11 Combustion chamber and piston bowlThe water passage around exhaust port in cylinder head is enlarged and the dividing wall between exhaust ports is extended for reducing exhaust gas temperature. The water around injector is supplied for cooling of injector tip. The long length is used for intensifying cooling around spark plug and super ignition spark plug of 12mm is for increasing ignition energy.Intake and exhaust system are optimized to increase volumetric and combustion efficiency. Intake air duct is shaped like straight pipe for minimizing resistance in higher intake flow. Variable intake manifold of barrel type is used, not only maximum torque but also maximum power is increased at the same time. Exhaust manifold, front muffler and catalytic converter are designed like Fig.12 for reducing light off time of catalytic converter and increasing performance. The distance between outlet of exhaust port and catalytic converter is shortened as short as possible and the weight and thickness of this exhaust manifold system is minimized for shorter light off tim