Characterization and Optimization of Coal‐Biomass Blends for Syngas Production as Alternative Transport Fuel Sources for Two‐Stroke Internal Combustion Engines in Tricycles‐Tuk Tuks in Kenya

Abstract

Conventional fuel sources, such as fossil fuels, have become unaffordable for the low end of the economy and thus the need for sustainable alternatives. Gasification of coal and biomass is considered as an alternative source for small‐sized engines, such as tricycles in Kenya. Mui basin coal is a low‐quality coal, available in Kenya, and blending with selected biomass (rice husks, Prosopis juliflora, and Hyphaene compressa) presents a new source of alternative transport fuel through cogasification and upgrading. The selected biomass samples were collected, air‐dried, and crushed to 60 μm and subjected to calorific determination, proximate, and ultimate analysis. Blending was done at various ratios weight by weight, while thermochemical determinations were conducted using the American Society for Testing and Materials (ASTM). The fixed carbon content was reported as 29.3 ± 5.51% for Mui basin coal, 21.1 ± 1.55% for rice husk, and 31.0 ± 1.00% for H. compressa. Blending was found to improve the hydrogen:carbon ratio with an average rate of 0.12 and decreased the sulphur and nitrogen content, leading to low emissions. The study revealed that calorific values of the fuel sources were as follows: Mui basin coal, 20.41 ± 0.15 MJ/kg; P. juliflora, 18.68 ± 0.17 MJ/kg; and H. compressa, 18.69 ± 0.00 MJ/kg, while rice husks had 12.95 ± 0.1 MJ/kg. Blending was also found to improve calorific values by average values of 0.4 MJ/kg for P. juliflora, 1.3 MJ/kg for H. compressa, and 2.28 MJ/kg for rice husk. The moisture content was reduced by 1–2% for all fuel sources; ash content was reduced by 33%, while the volatile matter was increased by 11% for P. juliflora, 7% for H compressa, and 0.2% for rice husks. The optimal blend of ratio 1 : 1 when cogasified produced syngas, which was upgraded through cleaning and cooling. The upgraded syngas had a moderate ratio of hydrogen to carbon monoxide with the right modification and retrofitting; it can be applied in internal combustion engines of tricycles‐“tuk tuks.” The study reveals that the optimal blending ratio of 1 : 1 for coal:biomass reduces the pollution ash content, increases calorific values, and enhances syngas fuel properties to moderate ratio.