Abstract Owing to the challenges associated with the application of synthetic/non-modified Botryococcus Braunii Microalgae Biodiesel (BBMB), its poor performance in CI engines has resulted in increased tendencies for non-commercialization of its fuel. The properties of a synthetic BBMB were controlled by acetylene addition. In this study, acetylene was induced with air at mass flow rates of 100, 150, 200 and 300 g/hr in order to monitor the combustion, emission and performance behaviour of a 4-stroke (Kirloskar AV1), 5.2 kW diesel engine with enhanced injection timing, in which the algal biodiesel was introduced as its main fuel. The obtained results compared favourably with those of a conventional dual-fuel CI engine in terms of combustion, emissions and performance. The brake thermal efficiency (BTE) of the acetylated biodiesel improved by 3, 4, 3.6 and 5% due to acetylene addition. NOx emissions were higher for the acetylated-biodiesel, whereas, the release of CO2, HC, and CO were seen to decrease due to the addition of acetylene. Based on the results, the performance, combustion and gaseous emissions of the biodiesel obtained from Botryococcus braunii improved as a result of adding acetylene thus making it a suitable replacement for the conventional diesel fuel used in CI engines.