Experimental investigation of direct injection charge cooling in optical GDI engine using tracer-based PLIF technique

Investigation of direct injection charge cooling effects is indispensable in design and development of new
combustion systems for Gasoline Direct Injection (GDI) engines. The charge cooling can be utilized to
increase engine volumetric efficiency or compression ratio. It can be employed to suppress pre-ignition
of highly boosted downsized engines or knocking combustion of naturally aspirated engines. The main
purpose of this work was to develop an experimental setup for quantitative measurements of charge
cooling during fuel injection process inside the combustion chamber of a GDI engine with optical access.
For this purpose a tracer-based two-line Planar Laser Induced Fluorescence (PLIF) technique was implemented
for the measurements. A specially designed Constant Volume Chamber (CVC) was utilized for
quasi in situ calibration measurement so in-cylinder charge temperature measurements can be achieved
independent of the photophysical model of dopant tracer. The thermometry technique was evaluated by
measurements of average in-cylinder charge temperature during compression stroke for both motoring
and firing cycles and comparing the results with temperature values calculated from in-cylinder pressure
data assuming a polytropic compression. The PLIF technique was successfully utilized to quantify the
extend of global temperature decrease as a result of direct injection charge cooling of two injection timings
of 90 and 250 CA ATDC and two injection quantities of 10 and 30 mg/cycle. Test results demonstrated
the capability of the two-line PLIF thermometry technique in quantitative study of direct
injection charge cooling effects.