Reducing emissions of an SI engine by alternative spark plugs with hydrogen addition and variable compression ratio

Abstract

As a consequence of the emissions-cheating scandals and more strict emission regulations enforce researchers to reduce emissions out and find alternative fuels for SI engines. For this purpose, various spark plugs are available in the market with different electrode materials. However, they have not been tested together with different engine parameters. Hence, emissions out from a variable compression spark-ignited engine with different spark plugs and hydrogen enrichment were the scope of this study. The tests were conducted with a four-stroke, single-cylinder, naturally aspirated, variable compression ratio (VCR) engine. Two different compression ratios (CR) of 8.5:1 and 10:1 at maximum brake torque (MBT) spark timing applied to assess the effects of different spark plugs and hydrogen usage at different engine loads. Copper, iridium and platinum spark plugs were tested for each experiment condition. Also, hydrogen was added through the intake manifold with flow rates of 0, 2 and 4 l/min to enhance the combustion of the VCR engine. Carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx) and unburned hydrocarbons (UHC) emission values were measured in this study. According to test results, with iridium and platinum spark plug usage, hydrogen addition and higher CR, the engine emitted lower CO and UHC at all engine loads. However, a higher amount of CO2 was emitted because of increased completeness of the combustion and the amount of NOx emissions rose due to increment in-cylinder temperatures. These variances were more apparent with platinum spark plug usage compared to the iridium spark plug. As a result, the usage of iridium and platinum spark plugs were shown lower incomplete emissions products out, except NOx emissions.