Turbulent Combustion Part 1

Turbulent - Spark-Ignition Engine Combustion Outline Essential features of the spark-ignition combustion process General features of combustion

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Spark-Ignition Engine Combustion Outline Essential features of the spark-ignition combustion process: General features of combustion: Flame Front and Structure Definition and Discussion of Burn Times Centering the Combustion Event for MBT Effect of Speed Effect of Load Effect of Plug Position Effect of Mixture Motions Effect of Geometry Effect of Diluents A very simple model of combustion What are the important physical phenomena? Does the model capture the important physics? What is missing?
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Spark-Ignition Engine Combustion Outline A correlation for ignition delay and 10-90% burn time What does it tell us about the general trends for combustion duration and MBT spark? What do experiments tell us about the relationship between burn time and MBT spark? Is there a correlation? How can we use it for: Understanding data? Understanding combustion stability? What is the concept of stability limited spark and why is it important? For understanding data and For setting up spark calibration tables. Engine heat transfer – what the textbooks don’t tell you but experimental data does. Review engine data on ISAC and BSFC
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Spark-Ignition Engine Combustion Outline Engine heat transfer –Implications of this view for engine efficiency. Engine knock: Review engine data real and anecdotal! What are the important design variables? Why are they important? The mythology behind engine knock! Burnrate effects Spark plug locations Why are engines more sensitive as they age?
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Motivation Discuss the Combustion Related Attributes of a Good Engine Design. What are these attributes? Excellent Idle Stability Capability to ignite and burn the mixture under highly dilute conditions (light loads or heavy EGR). Good drive-ability under transient conditions (might have momentary high residuals or lean mixtures). Capability to ignite and propagate a flame quickly across the chamber at high engine speeds. This is especially important for keeping exhaust temperatures low and thermal efficiencies high at speeds in excess of 5000 RPM. This is very critical for Formula 1 engines. Minimize time losses at high engine speeds yields: Excellent thermal efficiency Low exhaust temperatures for improved catalyst life.
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Combustion Attributes? In order to achieve the capability to ignite and propagate a flame reliably under dilute and high speed conditions we need: A high rate of flame propagation which is governed by: Combustion chamber shape, Spark plug location, In-cylinder fluid mechanics, Number of spark plugs, Mixture stratification, Delivering the “right” chemical composition of fuel, air and EGR to the engine cylinder. A reliable ignitability of the mixture which is governed
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This note was uploaded on 01/29/2012 for the course ME 444 taught by Professor Staff during the Fall '08 term at Michigan State University.

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Turbulent - Spark-Ignition Engine Combustion Outline Essential features of the spark-ignition combustion process General features of combustion

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