Engine Performances of Lean Iso-Octane Mixtures in a Glow Plug Heated Sub-Chamber SI Engine

Abstract

The overreliance on fossil fuels to generate energy is not sustainable because of their carbon emissions that are harming our environment. To substitute the fossil fuels with a more sustainable options, alternative fuels, such as carbon-free ammonia has been gaining worldwide attention. To allow the application of ammonia in internal combustion engines, its performance as an engine fuel need to be investigated. Ammonia as fuel has some shortcomings that can be outlined as slow combustion rate and corrosion due to the generation of hydrogen which makes it difficult to utilize in conventional internal combustion engines. In this study, an engine equipped with sub-chamber feature was used to overcome slow combustion rate of lean-burn condition of iso-octane/air mixture. Iso-octane was chosen as the fuel specifically since in lean-burn conditions, where the excess air ratio is near 1.8, its laminar burning velocity is similar to that of ammonia. The study was conducted using a single cylinder modified diesel engine which features spark plug and glow plug in a sub-chamber. The investigations varied the engine speeds (1000 and 1500 RPMs), glow plug voltages (6 V and 10 V), excess air ratios (1.4 to 1.8), and ignition timings (362 °CA to 365 °CA). The results suggested improved engine performances with a lower excess air ratio and higher glow plug voltage due to more complete and stable combustion. By increasing the engine speed, the lean burn limit was extended as seen from the improved engine performances. Because of the subchamber feature, advancing the ignition timing, with respect to the after top dead centre, resulted in lower engine performances. Larger excess air ratio was found to increase the sensitivity of the engine performances with the ignition timing. The brake mean effective pressure for all conditions has a coefficient of variation of less than 5%, indicating stable combustion. The results suggested that the current setup can be used to investigate ammonia blended fuel and direct ammonia combustion in future works.