Spray combustion simulation study of waste cooking oil biodiesel and diesel under direct injection diesel engine conditions

Spray combustion characteristics of waste cooking oil biodiesel (WCO) and conventional diesel fuels were simulated using a RANS (Reynolds Averaged Navier Stokes) based model. Surrogates were used to represent WCO and diesel fuels in simulations. N-tetradecane (C₁₄H₃₀) and n-heptane (C₇H₁₆) were used as surrogates for diesel. Furthermore for WCO, surrogate mixtures of methyl decanoate, methyl-9-decenoate and n-heptane were used. Thermochemical and reaction kinetic data (115 species and 460 reactions) were implemented in the CFD code to simulate the spray and combustion processes of the two fuels. Validation of the spray liquid length, ignition delay, flame lift-off length and soot formation data were performed against previous published experimental results. The modeled data agreed with the trends obtained in the experimental data at all injection pressures. Further investigations, which were not achieved in previous experiments, showed that prior to main ignition, a first stage ignition (cool flame) characterized by the formation formaldehyde (CH₂O) species at low temperature heat release occurred. The main ignition process occurred at high temperature with the formation of OH radicals. Furthermore, it was observed that the cool flame played a greater role in stabilizing the downstream lifted flame of both fuels. Increase in injection pressure led to the cool flame location to be pushed further downstream. This led to flame stabilization further away from the injector nozzle. WCO had shorter lift-off length compared to diesel as a result of its cool flame which being closer to the injector. Soot formation followed similar trends obtained in the experiments

Optimization of a low heat rejection engine run on oxy‑hydrogen gas with a biodiesel-diesel blend

This experimental investigation examines the combined effects of varying compression ratio (CR) and fuel injection parameters such as fuel injection pressure (FIP) and start of injection (SOI) / injection timing on the performance of a dual-fuel low heat rejection (LHR) engine run on oxy-hydrogen (HHO) gas with Jatropha biodiesel-diesel blend (JME20) as pilot fuel. The CR is varied from 16.5 to 18.5 in intervals of one, FIP is varied from 220 to 240 bar in intervals of 20 bar,and the SOI is varied from 24.5° to 27.5°CA bTDC in intervals of 1.5°CA. The performance, emission, and combustion characteristics of the dual-fueled LHR engine are studied, based on which the engine operating conditions are optimized. The results reveal that operating the LHR engine with 18.5 CR, 240 bar FIP, and 26°CA bTDC SOI using HHO in dual fuel operation mode with JME20 injected fuel gives better brake thermal efficiency (BTE) (6.6% higher than diesel) and combustion characteristics along with lower carbon monoxide (CO), hydrocarbon (HC), and smoke emissions. In contrast, a slight penalty in nitric oxide (NO) emissions is noticed irrespective of the engine operating conditions

Effects of ultra-high injection pressure and micro-hole nozzle on flame structure and soot formation of impinging diesel spray

The effects of ultra-high injection pressure (Pinj = 300 MPa) and micro-hole nozzle (d = 0.08 mm) on flame structure and soot formation of impinging diesel spray were studied with a high speed video camera in a constant volume combustion vessel. Two-color pyrometry was used to measure the line-of-sight soot temperature and concentration with two wavelengths of 650 and 800 nm. A flat wall vertical to the injector axis is located 30 mm away from the injector nozzle tip to generate impinging spray flame. Three injection pressures of 100, 200 and 300 MPa and two injector nozzles with diameters of 0.16 and 0.08 mm were used. With the conventional injector nozzle (0.16 mm), ultra-high injection pressure generates appreciably lower soot formation. With the micro-hole nozzle (0.08 mm), impinging spray flame shows much smaller size and lower soot formation at the injection pressure of 100 MPa. The soot formation is too weak to be detected with the micro-hole nozzle at injection pressures of 200 and 300 MPa. With eliminating the impact of injection rate on soot level, both ultra-high injection pressure and micro-hole nozzle have an obvious effect on soot reduction. Soot formation characteristics of impinging spray flame were compared with those of free spray flame using both the conventional and micro-hole nozzles. With the conventional nozzle, flat wall impingement deteriorates soot formation significantly. While soot formation characteristics of free spray flame with the micro-hole nozzle are not altered obviously by flat wall. Liquid length of the 0.16 mm nozzle is longer than the impingement distance and liquid length of the 0.08 mm nozzle is shorter than the impingement distance. Liquid impingement upon the wall is responsible for the deteriorated soot level of impinging flame compared to that of free flame with the conventional nozzle.Ultra-high injection pressure Micro-hole nozzle Impinging diesel spray Flame characteristics Soot formation Two-color pyrometry