Browsing by Author "Kyando, Michael"

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Compressed natural gas in aged internal combustion engines: performance, emissions, and challenges – a systematic review
(Elsevier Ltd., 2026-03-06) Kyando, Michael; Ntalikwa, Justin; Kivevele, Thomas
Compressed natural gas (CNG) offers significant emissions advantages over gasoline and diesel, yet most literature focuses on new or laboratory-optimized engines rather than the aged, retrofitted vehicles common in developing countries. With addition of other studies, the review followed PRISMA 2020 guidelines and a prospectively registered protocol (OSF) − https://osf.io/c8u7f/. Searches across Scopus, IEEE Xplore, and Google Scholar identified 816 records, of which 26 studies met inclusion criteria. CNG consistently lowered CO, HC, PM, and CO2 emissions, but retrofitted SI engines experienced 10–20% losses in power and torque due to methane’s low volumetric energy density and age-related declines in efficiency. High-mileage fleets showed methane-slip increases, catalyst deterioration, and lubricant oxidation, whereas optimized or dedicated CNG engines demonstrated improved thermal efficiency and fuel economy. Retrofit quality and calibration accuracy proved decisive in determining real-world outcomes. The findings highlight that CNG’s environmental and efficiency benefits are achievable but depend on proper engine design, maintenance, and regulatory support, especially in regions dominated by older vehicle fleets. This review provides the first systematic synthesis focused on aged, high-mileage, and retrofitted spark ignition (SI) and compression ignition (CI) engines operating on CNG, integrating evidence on performance, emissions, combustion behavior, methane slip, lubricant degradation, and catalyst aging. By comparing retrofitted and dedicated CNG engines against real-world aged engine across diverse regions, it reveals how engine architecture, retrofit quality, and accumulated mileage shape CNG outcomes and identifies the operational challenges and research priorities needed for durable, efficient, and low-emission operation.
Engine Mileage on Emissions of an Aged Retrofitted Spark Ignition Engine Fueled with Gasoline and Compressed Natural Gas
(Springer Nature, 2025-06-24) Kyando, Michael; Ntalikwa, Justin; Kivevele, Thomas
This study investigates the critical issue of rising emissions from aged retrofitted spark ignition (SI) engines, particularly as vehicle mileage increases. The objective is to analyze how engine mileage influences the emissions profiles of these engines when fueled by gasoline and compressed natural gas (CNG). Using an aged bi-fuel engine, the study measures emissions after every 5000 km of operation for both fuel types and compares them by EURO IV standard. As the engine mileage increases, key findings indicate that both gasoline and CNG engines meet EURO IV limits for carbon monoxide (CO) emissions, with gasoline engines showing a significant improvement over time (from 0.59 to 0.18%), while CNG engines consistently maintain lower emissions (0.12 to 0.02%). Carbon dioxide (CO2) emissions from gasoline engines increase as efficiency improves (from 14.4 to 15.6%), whereas CNG emissions show a notable decrease from 15.93 to 11.33%. Additionally, hydrocarbon (HC) emissions exhibit a similar trend, reflecting enhanced combustion efficiency in gasoline engines compared to CNG. Nitrogen oxide (NOx) emissions present a challenge for gasoline engines, which can exceed EURO IV limits, while CNG engines experience a more moderate increase in NOx levels. These findings highlight the environmental advantages of CNG as a cleaner fuel alternative and underscore the compliance challenges faced by both fuel types under stringent emissions regulations, emphasizing the importance of engine mileage in emissions management.