Analysis of Ignition and Combustion in Otto Lean-Burn Engines with Prechambers

Abstract

Otto-engines in which the combustion chamber has richer fuel/air mix close to the ignition source and leaner charge further away from the ignition source are often called "stratified charge engines". Stratified charge can be used to increase the combustion speed in an internal combustion engine and thereby enable the engine to run on a fuel/air mix that would normally burn too slowly or not burn at all. The use of prechambers is one way to obtain stratified charge.

This thesis presents and uses methods for studying a prechamber more or less indepently from the rest of the engine.

When the prechamber is studied like an engine of itself, then the output of the "engine" is not mechanical power, but rather one or more hot jets into the main chamber. "Prechamber efficiencies" can be defined based on how much of the initial chemical energy is delivered as kinetic or thermal energy into the main chamber. Models of other important characteristics including the jet length and duration are also presented and used.