In general, GDI engines operate with stratified mixtures at part-load conditions
enabling increased fuel economy with high power output, however, with a
compensation of increased soot emissions at part-load conditions. This is mainly
due to improper in-cylinder mixing of air and fuel leading to a sharp decrease
in gradient of reactant destruction term and heat release rate (HRR), resulting
in flame quenching. The type of fuel injector and engine operating conditions
play a significant role in the in-cylinder mixture formation. Therefore, in this
study, a CFD analysis is utilized to compare the effect of stratified mixture
combustion with multi-hole solid-cone and hollow-cone injectors on the
performance and emission characteristics of a spray-guided GDI engine.
The equivalence ratio (ϕ) from 0.6 to 0.8 with the constant
engine speed of 2000 rev/min is considered. For both injectors, the fuel
injection pressure of 200 bar is used with 60° spray-cone angles. For lean
boosting conditions, intake pressures of 1 bar, 1.2 bar, and 1.4 bar are
maintained for 0.8 equivalence ratio cases for both injectors. Results from the
CFD analysis are compared with those of the available experimental results with
good agreement. Analyzing the results, naturally aspirated and intake boosting
conditions for ϕ of 0.8, mixture distribution and flame
propagation for the multi-hole solid injector are better than hollow-cone
injector. Also, for the ϕ of 0.8, naturally aspirated mode, the
soot emissions by the hollow-cone injector are higher by about 90%, and the
NOx emissions are higher by about 19% compared to that of the
multi-hole solid-cone injector. Under boosted intake pressure conditions, for
the hollow-cone injector, the soot emissions are higher by about 97%–99%, and
NOx emissions are higher by about 7%–6% compared to the
multi-hole solid-cone injector. Also, HC and CO emissions are considerably lower
for the hollow-cone injector than that of the multi-hole solid-cone
injector.
