Improvements in Dual-Fuel Biodiesel-Producer Gas Combustion at Low Loads through Pilot Injection Splitting

In dual-fuel engines, a combustible mixture of air and generally a gaseous fuel is ignited, thanks to the injection and autoignition 6 of a small amount of liquid fuel. It is well-known that dual-fuel engines suffer from poor combustion when operated at low loads. This 7 behavior, due mainly to the presence of an overlean mixture into the combustion chamber, leads to unacceptably high levels of carbon 8 monoxide and unburned hydrocarbons emitted at the exhaust. In order to solve this problem a possible solution could be to split the pilot 9 injection of liquid fuel into two split injections, the second having the function of boosting the combustion of gaseous fuel also during the late 10 combustion phase. In this paper this solution has been implemented on a diesel common rail single cylinder research engine converted to 11 operate in dual-fuel mode. The composition of the gaseous fuel, indirectly injected, simulated a typical producer gas. The liquid fuel used 12 during the experiments was biodiesel, injected by means of a common rail injection system. The first section of results describes the tests run 13 for comparison purposes, performing only one pilot biodiesel injection and varying its timing on a wide range. The second section of results 14 then presents the tests run for different timings, varied on a wide range, of the first split injection, and different dwells between the first and the 15 second injections. The engine behavior has been discussed in terms of heat release rate, fuel conversion efficiency, and nitric oxides, total 16 hydrocarbons, and carbon monoxide emission levels at the exhaust. The results demonstrate that splitting the pilot injection leads to an 17 increase of fuel conversion efficiency and a reduction of both total hydrocarbons and carbon monoxide. This final result allows to state 18 that splitting the pilot injection is an effective way for sustaining the gaseous fuel combustion in dual-fuel engine late during the combustion 19 phase.