Published on March 7, 2014
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• Gasoline direct-injection engines generate the air/fuel mixture in the combustion chamber. • During the induction stroke, only the combustion air flows through the open intake valve. • The fuel is injected directly into the combustion chamber by special fuel injectors.
Major Objectives of the GDI engine Ultra-low fuel consumption that betters that of even diesel engines Superior power to conventional MPI engines
WHY NOT CARBURETTOR? Carburetor has following disadvantages Vapor lock Perfect air/fuel mixture cannot be obtained Lack of throttle response Low volumetric efficiency Icing – problem in aircraft engines Mechanical device Compromises on emission
Transition of fuel supply
Major characteristics of the GDI engine 1. Lower fuel and higher output consumption Optimal fuel spray for two-combustion mode Ultra-lean Combustion Mode Superior Output Mode
2. The GDI engines foundation technologies In-cylinder Airflow
Realization of lower fuel consumption Basic Concept • In conventional gasoline engines, dispersion of an air-fuel mixture with the ideal density around the spark plug was very difficult. However, this is possible in the GDI engine. Furthermore, extremely low fuel consumption is achieved because ideal stratification enables fuel injected late in the compression stroke to maintain an ultra-lean air-fuel mixture.
• As a result, extremely stable combustion of ultralean mixture with an air-fuel ratio of 40 (55, EGR included) is achieved as shown below.
Combustion of Ultra-lean Mixture In conventional MPI engines, there were limits to the mixtures leanness due to large changes in combustion characteristics. However, the stratified mixture of the GDI enabled greatly decreasing the air-fuel ratio without leading to poorer combustion. For example, during idling when combustion is most inactive and unstable, the GDI engine maintains a stable and fast combustion even with an extremely lean mixture of 40 to 1 air-fuel ratio (55 to 1, EGR included)
Vehicle Fuel Consumption Fuel Consumption during Idling The GDI engine maintains stable combustion even at low idle speeds. Moreover, it offers greater flexibility in setting the idle speed. Compared to conventional engines, its fuel consumption during idling is 40% less.
Emission control • However, in the case of GDI engine, 97% NOx reduction is achieved by utilizing high-rate EGR (Exhaust Gas Ratio) such as 30% that is allowed by the stable combustion unique to the GDI as well as a use of a newly developed lean-NOx catalyst.
Realization of Superior Output Basic concept To achieve power superior to conventional MPI engines, the GDI engine has a high compression ratio and a highly efficient air intake system, which result in improved volumetric efficiency.
Improved Volumetric Efficiency • Compared to conventional engines, the Mitsubishi GDI engine provides better volumetric efficiency. • The upright straight intake ports enable smoother air intake. • And the vaporization of fuel, which occurs in the cylinder at a late stage of the compression stroke, cools the air for better volumetric efficiency.
Increased Compression Ratio • The cooling of air inside the cylinder by the vaporization of fuel has another benefit, to minimize engine knocking. This allows a high compression ratio of 12, and thus improved combustion efficiency
GDI Vehicles BMW Ford EcoBoost General Motors 2.0L Ecotec Hyundai Theta Lexus Mazda Speed Direct Injection Spark Ignition Mitsubishi Gasoline Direct Injection Volkswagen FSI Fuel Stratified Injection
Gasoline direct injection (GDI) engine technology has received considerable attention over the last few years as a way to significantly improve fuel efficiency without making a major shift away from conventional internal combustion technology. In many respects, GDI technology represents a further step in the natural evolution of gasoline engine fueling systems.
References • http://personales.upv.es/~jlpeidro/gdi/gdi.ht m • http://auto.howstuffworks.com/directinjection-engine.htm • http://en.wikipedia.org/wiki/Gasoline_direct_ injection • Video- Youtube.com
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