Experimental Studies of a Low Heat Rejection Engine Run in Dual-Fuel Mode

Abstract

Hydrogen is perceived to be a potential sustainable energy source of the future due to some of its favorable properties such as its carbon-free nature, high calorific value, wider flammability range, and high burning velocity. However, the problems associated with the storage of hydrogen, and the limited availability of hydrogen to meet the demand has compelled the research community to identify other possible solutions. Oxy-hydrogen gas (HHO) is a carbon-free fuel similar to hydrogen which can be produced by the water electrolysis process. Hence, this research work explores the possibility of using HHO gas also known as Brown gas as an alternative to hydrogen in a low heat rejection (LHR) engine under dual-fuel mode (DFM). A biodiesel-diesel blend (JME20) containing 20% Jatropha methyl ester (JME) and 80% diesel on a volume basis is used as a pilot fuel, while HHO gas is used as an inducted fuel in the intake manifold of a compression ignition (CI) engine. For the investigation, a single-cylinder, naturally aspirated, direct injection (DI) diesel engine developing a power output of 4.4 kW at a constant speed of 1500 rpm is converted to DFM. The engine behavior in terms of combustion, performance, and emission parameters of the dual-fuel engine is assessed without and with fuel and engine modifications. HHO gas is generated by the electrolysis of water from an in-house fabricated wet-cell electrolyzer. In the first set of experiments, baseline data of conventional CI engine behavior in terms of the combustion, performance, and emissions are collected for diesel/JME20 at optimized engine conditions in the single fuel mode. In the next set of experiments, the engine is modified to DFM to study the effect of using HHO gas as inducted fuel with diesel/JME20 as pilot fuels. The combustion, performance, and emission characteristics of the dual-fuel engine run on diesel/JME20+HHO are evaluated and compared with baseline data and validated with theoretical combustion analysis of the dual-fuel engine is carried out by using MATLAB coding. The dual-fuel engine is modified to run in the low heat rejection (LHR) mode by replacing the normal piston with the Yitira Stabilized Zirconia (YSZ)/ YSZ+CeO2 (Cerium Oxide) coated pistons to reduce heat loss from the engine. Then experiments are conducted on retrofitted dual-fuel LHR engine. The results of the YSZ+CeO2 coated piston-fitted LHR engine run on JME20+HHO exhibited higher BTE than YSZ coated piston engine operation. The maximum CO, HC, and smoke emissions with the YSZ+CeO2 coated piston-fitted engine operation in the DFM with JME20+HHO, are found to be lower by about 44.1%, 46.7%, and 21.5%, respectively, compared to baseline data at full load while nitric oxide (NO) emissions were higher by 19.17%. In the next stage of experiments, the JME20+HHO dual-fueled LHR engine’s operating conditions will be optimized for best performance. The operating conditions of are optimized by the collated data from experiments at varying compression ratio (CR) from 16.5 to 18.5, varying fuel injection pressure (FIP) from 220 to 240 bar, and varying the start of injection (SOI) / injection timing from 24.5° to 27.5°CA bTDC. The results also reveal that operating the dual-fueled LHR engine with 18.5 CR, 240 bar FIP, and 26°CA bTDC SOI is a good strategy for running the dual-fuel engine on JME20 with HHO induction because of better BTE (6.6% higher than diesel) and combustion characteristics and lower CO, HC, and smoke emissions. In contrast, a penalty in NO emissions is noticed irrespective of the engine operating conditions. Further investigations are carried out to address the higher NO emissions noticed in optimized JME20+HHO duel-fueled LHR engine behavior by doping antioxidants with pilot fuel. Antioxidants at concentrations of 500, 1000, 1500, and 2000 ppm are doped in the pilot fuel (JME20 blend). The pilot fuel was doped with two chemical antioxidants, N-Isopropyl-N'-phenyl-1,4-phenylenediamine (IPPD) and N, N'-Diphenyl-p phenylenediamine (DPPD), as well as two natural antioxidants made from biomass, Alibizia lebbeck leaf powder (ALLP) and Pongamia pinnata leaf powder (PPLP). The combustion, performance, and emissions of the test dual-fuel engine run on antioxidant-doped JME20+HHO are assessed and compared with those of baseline data. The results revealed that a 2000 ppm DPPD-doped JME20+HHO operation shows 5.6% lower BSEC, 32.3% lower CO, 35.3% lower HC, and 13.9% lower smoke as compared to baseline diesel data at full load. Among all the antioxidants, PPLP antioxidant-doped JME20+HHO operation shows a 10% NO emission reduction at 2000 ppm concentration compared to JME20+HHO operation. This research work identified the optimized LHR engine (18.5 CR, 240 bar FIP, and 26°CA bTDC SOI) for HHO gas induction with PPLP antioxidant-doped JME20 operation. The corresponding results showed an 9.13% higher HRR, 6.09% lower BSEC, 30.8% lower CO, 33.3% lower HC, and 8.31% lower smoke compared to baseline diesel data at full load.