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Effect of the Supply of the Mixture During Injection Into the Intake Manifold
ISSN: 0148-7191, e-ISSN: 2688-3627
Published January 01, 1984 by SAE International in United States
Thermodynamic considerations provide a good overview of orders of magnitude in mixture preparation. A rough calculation at 20°C ambient temperature and with thorough mixing with air reveals that approximately 70% of the gasoline evaporates. Through polytropic compression up to the point of ignition it is possible for a further 10% of the gasoline to evaporate. The remainder of the gasoline must be evaporated by the hot intake manifold and the hot combustion chamber. The problem is alleviated by the property of the hydrocarbons since the specific heat of vaporization converges toward zero with increasing pressure and temperature.
Mechanical atomization both with the K-Jetronic nozzle and the L-Jetronic valve provides most of the mixture preparation; additional air shrouding produces slight advantages in idle consumption and greater advantages in smoothness of running in the range close to idle.
Shifting the point of injection upstream and away from the inlet valve is impractical due to the necessity of acceleration enrichment.
Advancing the moment of injection to before the intake stroke in the case of sequential injection likewise improves mixture preparation with the L-Jetronic. There are further advantages to sequential injection.
Stratification in the open combustion chamber is still an unsolved problem.