MODERN TRENDS IN AUTOMOBILES
GASOLINE DIRECT INJECTION ENGINES By Sumeet Gujral
DIRECT INJECTION TECHNOLOGY
Precise control of charge stratification leading to burning of ultra lean mixtures. No need of throttle and hence no Pumping Loss. No need of a Carburetor
Straight Upright Intake ports. Curved top pistons. High pressure fuel pump. High pressure swirl injectors.
TWO MODES OF COMBUSTION
Lean Mode: Output Mode
ULTRA LEAN MODE
During normal driving conditions when there is no acceleration.
SUPERIOR OUTPUT MODE
Combustion of homogenous charge. Higher power output than even conventional engines.
TORQUE Vs ENGINE SPEED
TWO STAGE MIXING CONCEPT
1ST STAGE: ¼ of the total volume of fuel is injected during intake stroke. 2nd STAGE: Remaining fuel is injected during later stages of compression.
BENEFITS OF TWO STAGE MIXING
BENEFITS OF GDI ENGINES
Better Thermal Efficiency. Better Volumetric Efficiency. Max Compression Ratios can be employed. Very Lean Mixtures with the Air: Fuel ratio of the order of 40:1 can be effectively used. Does not require a carburetor. Emission of exhaust gases is best.
LIMITATIONS OF GDI ENGINES
Higher NOX emission. To reduce NOX emission if EGR is used, it increases both cost as well as weight. Can not be used at those places where Sulpher content is high in gasoline.