Sliding Mode Control of Air Path in Diesel-Dual-Fuel Engine

In diesel-dual-fuel engine, CNG is injected at the intake ports and diesel fuel is injected at the cylinders. As a result of using CNG as main fuel, smaller amount of diesel is used mainly for ignition, resulting in lower fuel cost. However, stricter air path control is required because the engine now operates partly as a port fuel injection engine and partly as a diesel engine. As is evident from engine calibration, desired MAP and MAF have more abrupt change with wider range than those of diesel engine. In typical commercial truck, MAP and MAF are controlled separately using traditional controller such as PID with marginal control performance. Recently, more researchers have combined the control of MAP and MAF together as multivariable problem because both quantities reflect the behavior of the air path. In this paper, multivariable sliding mode control (SMC) is implemented in two-approaches, a model-reference-based and an integrator-augmented based. The diesel-dual-fuel engine was converted from a diesel engine and used in the engine test bed. Throttle and EGR valve were actuated to regulate MAP and MAF at their respective set points. Experimental results at an engine speed of 2000 rpm and 20% pedal showed that the two proposed algorithms delivered good tracking performance with fast action. The MAP and MAF responses were able to track their desired values with 2.5 seconds settling time and less than 10% overshoot. The integrator-augmented SMC had more response accuracy than the model-reference SMC but with more chattering.