Experimental investigation of direct injection dual fuel of n-butanol and biodiesel on Intelligent Charge Compression Ignition (ICCI) Combustion mode

To achieve ultra-high efficiency and low emissions over the full engine operating range, the intelligent charge compression ignition (ICCI) combustion mode was firstly proposed. In ICCI mode, by real-time control over the injection strategies of two independent direct injection systems (including fuel proportions, injection pressure, timing and duration), the concentration and reactivity stratifications of the air-fuel mixture can be flexibly adjusted. Therefore, in this paper, an experimental study was conducted on a single cylinder diesel engine to research the working mechanism of ICCI mode fueled with biodiesel and n-butanol. Experimental results showed that, the n-butanol/biodiesel ICCI combustion mode had great potential to improve engine efficiency and reduce its emissions. At medium load, the early biodiesel injection timing (SOI2) can shorten the combustion duration and improve the indicated thermal efficiency (ITE), and the maximum ITE can reach 50.7%. As the butanol energy ratio increased, the nitrogen oxides (NOx) emissions could be reduced due to the reduction of local high temperature, while NOx emissions were always at low level and it can meet Euro 6 emission standards. The butanol injection pressure had significant effect on the combustion and emission characteristics of the ICCI mode, properly increasing the butanol injection pressure can improve the ITE and reduce emissions, however, excessive butanol injection pressure deteriorates the combustion process, increased the hydrocarbon and carbon monoxide emissions. In general, the butanol-biodiesel ICCI mode can achieve stable combustion under different loads while ensuring high efficiency and ultra-low emissions with a single injection of biodiesel at low/medium loads and two injections of biodiesel at high load.