Optical diagnostics on spray characteristics and soot volume fraction of n-butanol, Diesel and hydrotreated vegetable oil blends in a constant volume combustion chamber 2019-01-0019

The effect of the addition of n-butanol in fossil Diesel or hydrotreated vegetable oil (HVO) on spray, flame and soot characteristics were investigated in a high temperature high pressure constant volume combustion chamber. Backlight illumination method was employed to capture liquid and vapor phase spray images via a high speed camera. Flame lift-off length (LOL) and ignition delay were analyzed on the base of OH* chemiluminescence images. Laser extinction diagnostics were deployed to measure the spatially and temporally resolved soot volume fraction. The spray experiments were performed by fuelling neat n-butanol (nBu), fossil Diesel (D) and HVO (H) and their blends under non-combusting (623K) and combusting (823K) conditions at the fixed ambient air density 26 kg/m3. Scania 0.19 mm single straight hole injector and Scania XPI common rail fuel supply system were used to produce 120 MPa, 180 MPa and 250 MPa injection pressure in the study. To evaluate the effect of cetane number (CN) on combustion and soot emissions, the use of di-tertiary-butyl peroxide (DTBP) provided the possibility to boost the blends’ CN without great change of their composition. The selected blends were also tested in a single cylinder heavy duty (HD) engine at the condition similar to the combusting condition of the spray measurement. The results indicate that HVO and its blends have the longest liquid spray penetration at steady state. Ignition delay is influenced by CN and volatility of the fuel and injection pressure. The soot volume fraction of butanol blends shows a great reduction, because of their oxygen containing and better volatility, compared to that of Diesel fuel.