A review of combustion geometry profiles in biodiesel-fueled compression ignition engines: technical insights into combustion, performance, and emission characteristics

For improved efficiency and lower emissions in biodiesel fueled engine operation, either fuel properties or engine design parameters are adjusted. However, improving biodiesel characteristics is often difficult and expensive. In contrast, engine modifications are typically most cost effective and therefore more commonly used. One of the most important modifications is altering the geometry of the combustion chamber (CC), which has a vital influence on engine performance and emissions. Even slight changes in CC geometry have been shown to significantly improvement in the behaviour of biodiesel fueled engines. This review explores several CC geometries, such as shallow depth, trapezoidal, re-entrant, and toroidal etc. It addresses research gaps in prior studies by examining how these CC geometries affect the performance, emissions, and combustion characteristics of biodiesel powered engines. The review finds that the re-entrant bowl piston design is particularly effective for enhancing swirl and turbulent kinetic energy during the compression stroke. Toroidal combustion chambers (TCCs) are considered one of the most promising alternatives for biodiesel operation, as they reduce ignition delay by at least 10%. Compared to other geometries, TCCs enhance combustion, increase thermal efficiency, and lower fuel consumption, resulting in improved engine output. Shallow depth CC are less frequently investigated in research but may be suitable for large vehicles operating at low speeds. Since biodiesel-fueled engines are well-suited for heavy-duty, low-speed applications, shallow depth CC could offer an appropriate design solution.