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The Fuel stratification process has been investigated in the cylinder of an axially stratified lean burn engine by visualizing fuel behavior. Planar laser light sheet from an Nd:YAG laser has been illuminated through the transparent quartz cylinder of a single cylinder optical engine. Mie scattered light has been captured through the quartz window in the piston head with an ICCD camera. Fuel has been replaced with an ethanol droplets to utilize an atomized fuel spray for visualization purposes. Swirl ratios have been varied by changing cylinder heads with different swirl numbers and injection time has been varied to find the effect of fuel stratification. A higher lean mixture limit was achieved when the fuel remained at the combustion chamber as stratified with the proper combination of fuel injection timing swirl flow.

The mechanism of axial stratification was investigated in a port injection SI engine. The port swirl and tumble number characterized the ports. The experiment consisted of a steady flow rig test for defining flow characteristics, engine test for finding lean misfire limit, fuel behavior tracing in a steady flow rig for the understanding basic stratification, fuel motion visualization in motored engine for the investigating real stratification process and flame capturing under known stratified conditions. The results show that not only swirl but also tumble affects axial stratification with the interaction of injection timing. It was also observed that stable initial flame improved engine stability by stratification, but the flame propagation pattern and direction was not affected by stratified condition, load, air-fuel ratio and fuel phase but by bulk in-cylinder flow pattern.

A commercial DOHC 4-Cylinder sequential MPI SI engine was modified as a research single cylinder engine. And four kinds of cylinder head with the same combustion chamber geometry have been used to induce in-cylinder flow of different swirl ratio. To investigate the effect of injection timing on the lean misfire limit (LML), experiments have been made at selected engine speeds for each cylinder head. Fuel injection timing was varied while running the engine at a constant speed. And the LML was defined as the mixture ratio at which engine speed deviates more than 10 rpm from the present speed resulting in the engine instability which might be causing from misfire or partial combustion. Results show that LML or stability of engine is not affected by engine speed because early flame stability is dominated not by turbulence but by AFR around the spark plug at spark timing. Stratification of mixture resulting from port swirl and injection timing were shown to govern the LML.