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Biogas is a renewable alternative fuel for internal combustion engines that has several advantages over conventional fuels, including lower costs and reduced levels of harmful emissions. In particular, it exhibits a neutral recirculation loop for carbon dioxide (CO 2 ), which is one of the main causes of global warming. In this study, we investigated biogas fuels with various compositions using a micro co-generation engine system. The ratio of methane to CO 2 and engine load were varied, and the intake air and fuel flow rates were controlled to change the equivalence ratio. The results show that for a given engine load, the ignition delay and combustion period increased with CO 2 content, and the combustion speed decreased. The fuel consumption increased slightly with CO 2 content; however, the thermal efficiency improved using a lean burn strategy, resulting in lower nitrogen oxide (NO X ) emission, and moreover, the use of biogas with the stoichiometric air–fuel ratio appears effective in reducing NO X emissions and can improve the fuel economy at higher loads. [ABSTRACT FROM AUTHOR]

Biogas, a renewable and alternative energy, has recently gained attention as an environmentally friendly fuel for power generation in internal combustion (IC) engines. This study aimed to investigate the effect of the carbon dioxide (CO 2) to methane (CH 4) ratio in a dual-fuel gas engine. It is known that gaseous fuel combustion at high loads is accompanied by knocking if an appropriate combustion controlling strategy is not applied. Therefore, premixed mixture ignition in the end-gas region (PREMIER) combustion was proposed under high load conditions. Experiments were carried out using a dual-fuel gas engine under supercharged conditions, with an intake pressure of 200 kPa. Simulated biogas consisting of CH 4 and CO 2 was used as a primary fuel and diesel was used as a pilot fuel. The pilot fuel injection timing was varied during the experiments. The indicated mean effective pressure (IMEP) and thermal efficiency increased as injection timing was advanced. With the addition of CO 2 , the thermal efficiency of PREMIER combustion was slightly increased, although the IMEP was slightly decreased. The unburned gas temperature for PREMIER combustion increases as a function of the CO 2 content of the mixture. Due to compression by flame propagation, high unburned gas temperatures in dual-fuel gas engines are important for achieving autoignition inside the end-gas region under PREMIER combustion conditions. [ABSTRACT FROM AUTHOR]

• The PI value of PREMIER combustion was proposed to characterize the end-gas autoignition. • End-gas autoignition of a premixed mixture occurred earlier with advancing injection timing. • The heat release amount of end-gas autoignition increased when more autoignition in the end-gas region occurred. • The PREMIER operation mode improved thermal efficiency and IMEP. To improve the thermal efficiency of internal combustion engines at high loads, premixed mixture ignition in the end-gas region (PREMIER) combustion is proposed as a precursor to knocking. In the current work, a pilot fuel-ignited dual-fuel gas engine was operated at constant speed under different intake pressures (101, 150, and 200 kPa). A simulated biogas was served as the primary fuel and diesel as the pilot fuel. The maximum mean effective pressure and thermal efficiency were evident during PREMIER operation because of autoignition in the end-gas region. Similar to knocking combustion, PREMIER combustion features two stages but neither pressure oscillation nor a rapid pressure rise is observed. We here define a new parameter, the PREMIER intensity (PI), which reflects the strength of PREMIER combustion. As the injection timing was advanced and the pressure boosted, more cycles underwent end-gas autoignition; the associated heat release increased and, consequently, the PI value rose. When the pressure and temperature of a premixed fuel mixture rose as injection timing was advanced, end-gas autoignition commenced earlier. The end-gas autoignition delay became shorter as intake pressure was increased and injection timing advanced. [ABSTRACT FROM AUTHOR]