Reactivity controlled compression ignition (RCCI) is found promising low temperature combustion mode that has recorded tremendous success towards improving thermal efficiency and reducing NOx and soot emissions to nearly zero but has high specific fuel consumption, unburned hydrocarbon (UHC) and carbon monoxides (CO) emissions. Besides, RCCI requires combustion phasing control and loads extension to higher levels. Numerous researchers employed different strategies like use of exhaust gas recirculation (EGR) rate and dual fuel control to improve RCCI combustion performance and emission characteristics but little attention was paid to some strategies such as use of dual direct injection, oxygenated biofuels, and fuel additives. In addition, most of the researchers do consider one strategy without exploring the combined effects of many strategies at a time; hence, the technique requires combined strategies and methods for effective control and improved performance. This paper reviewed previous research activities and recent reviews on RCCI engine performance and emission characteristics with the view to finding information on current RCCI combustion methods and strategies while identifying its shortcomings. Eventually, some challenges of RCCI that affects its adaptability for effective commercialization were identified with respect to strategies integration and areas that require more efforts for more advances in the combustion mode were suggested.

High unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions, on account of the premixed air-fuel mixture entering the crevices and pre-mature combustion, are setbacks to reactivity-controlled compression ignition (RCCI) combustion at a low load. The influence of direct-injected B5 and port injection of biogas at the intake valve was, experimentally, examined in the RCCI mode. The port injection at the valve was to elevate the temperature at low load and eliminate premixing for reduced pre-mature combustion and fuel entering the crevices. An advanced injection timing of 21° crank angle before top dead centre and fraction of 50% each of the fuels, were maintained at speeds of 1600, 1800 and 2000 rpm and varied the load from 4.5 to 6.5 bar indicated mean effective pressure (IMEP). The result shows slow combustion as the load increases with the highest indicated thermal efficiency of 36.33% at 5.5 bar IMEP. The carbon dioxide and nitrogen oxides emissions increased, but UHC emission decreased, significantly, as the load increases. However, CO emission rose from 4.5 to 5.5 bar IMEP, then reduced as the load increases. The use of these fuels and biogas injection at the valve were capable of averagely reducing the persistent challenge of the CO and UHC emissions, by 20.33% and 10% respectively, compared to the conventional premixed mode.

Little attention is given to the impacts of chemical exposure on construction workers' health and the environment. Out of 302 reported and analyzed cases to the Department of Safety and Health (DOSH) from 2010 to 2019, about 0.66% are exposure to hazardous chemicals. This paper developed an AHP model for the factors and sub-factors of chemical exposure and determined their relative weights and priorities. Worker's unsafe actions have a maximum weight of about 80.98% for the significant factors based on the proposed model, followed by unsafe site conditions of 10.89% and management factors of 8.13%. Financial constraint carries the most weight with 20.22% for management factors, lack of or improper on-site storage for hazardous chemicals, incorrect labelled or unlabeled signs indicating hazardous chemicals, incorrect labelled or unlabeled containers carrying hazardous chemicals and lack of or improper on-site disposal of used hazardous chemicals with 16.13% each carry the most weight for unsafe site conditions. Rushing to complete the job and unauthorized access to the hazardous chemicals carry the most weight, with 17.24 % each. This study can help safety practitioners understand the factors and sub-factors responsible for chemical exposure and how they can decrease fatal accidents on-site.