Advanced strategies to reduce harmful nitrogen-oxide emissions from biodiesel fueled engine

Advanced techniques have shown an effective approach to reducing nitrogen oxide (NOx) emissions from biodiesel-fueled engines. The primary concern is higher NOx emissions using biodiesel due to its different physio-chemical fuel properties and higher in-cylinder combustion temperatures than diesel. This study aims to scrutinize the existing literature on NOx forming origins from biodiesel and present the state-of-the-art literature on reduction technologies, identify research gaps and introduce further developments to the research opportunities. Accordingly, the present review has organized the technologies into three categories: pre-combustion, combustion, and post-combustion techniques. In addition, the pros and cons of each technique are presented by identifying their role using combustion characteristics. The study identifies that ignition delay and combustion duration are the major factors to consider in reducing NOx emissions. Applying innovative tactics to modify the fuel, chamber, and injection parameters prolongs the ignition delay and combustion duration, thereby reducing NOx emissions. Furthermore, exhaust gas after-treatment systems with novel catalytic convertors have shown a strong capability of reducing NOx emissions. The findings also indicate significant reductions in NOx emissions from biodiesel with provided technologies; however, a clear roadmap is needed to integrate these technologies for sustainable application. The study concludes that emulsion techniques, low-temperature combustion strategies, retarded injection timing, and exhaust gas after treatment have shown significant NOx reduction through reduced peak temperature rates. The study recommends further investigation on reactive controlled combustion techniques as they directly impact NOx emission, and their results comparisons will give a clear understanding for deriving better commercial options.