Biodiesel is a suitable alternative to diesel because of its carbon neutrality,
renewability, lubricity, and lower pollutant emissions. However, extensive
research indicates higher oxides of nitrogen (NOx) emissions with
biodiesel. A practical method to combat this problem is utilizing water and
biodiesel as emulsions. The effect of biodiesel-water emulsion in high-pressure
fuel injection systems is not fully explored in the existing literature. The
present study addresses this research gap by utilizing biodiesel-water emulsions
in a modified light-duty diesel engine. The governor-controlled injection system
was adapted to a fully flexible electronic system capable of high-pressure
injection. Unlike other literature studies, the fuel injection timings were
optimized with biodiesel-water emulsions to maximize brake thermal efficiency
(bte) at every load condition. In a novel attempt, the biodiesel source, i.e.,
raw Karanja oil (RKO), a triglyceride, was utilized as the surfactant to
stabilize the biodiesel-water emulsions containing 6%, 12%, and 18% water. The
emulsions reduced the ignition delay and cylinder pressures, with less-intense
premixed combustion and a more significant diffusion phase combustion than
biodiesel. The emulsions also present a delayed combustion phasing following the
injection timing trends. Among the tested emulsions, at 5.08 bar brake mean
effective pressure (BMEP), 18% biodiesel-water emulsion resulted in an 18%
reduced brake specific fuel consumption (bsfc), 5% increase in bte, 30% and 7%
mitigation in NOx and smoke levels, with an increase of 10% and 28%
for unburned hydrocarbon (HC) and carbon monoxide (CO) emissions.
