Modeling and control of fuel distribution in a dual-fuel internal combustion engine leveraging late intake valve closings

Abstract

In internal combustion engines, cycle-to-cycle and cylinder-to-cylinder variations of the combustion process have been shown to negatively impact the fuel efficiency of the engine and lead to higher exhaust emissions. The combustion variations are generally tied to differences in the composition and condition of the trapped mass throughout each cycle and across individual cylinders. Thus, advanced engines featuring exhaust gas recirculation, flexible valve actuation systems, advanced fueling strategies, and turbocharging systems are prone to exhibit higher variations in the combustion process. In this study, the cylinder-to-cylinder variations of the combustion process in a dual-fuel internal combustion engine leveraging late intake valve closing are investigated and a model to predict and address one of the root causes for these variations across cylinders is developed. The study is conducted on an inline six-cylinder heavy-duty dual-fuel engine equipped with exhaust gas recirculation, a variable geometry turbocharger, and a fully flexible variable intake valve actuation system. The engine is operated with late intake valve closure timings in a dual-fuel combustion mode in which a high reactivity fuel is directly injected into the cylinders and a low reactivity fuel is port injected into the cylinders. The cylinder-to-cylinder variations observed in the study have been associated with the maldistribution of the port-injected fuel, which is exacerbated at late intake valve timings. The resulting difference in indicated mean effective pressure between the cylinders ranges from 9% at an intake valve closing of 570° after top dead center to 38% at an intake valve closing of 620° after top dead center and indicates an increasingly uneven fuel distribution. The study leverages both experimental and simulation studies to investigate the distribution of the port-injected fuel and its impact on cylinder-to-cylinder variation. The effects of intake valve closing as well as the impact of intake runner length on fuel distribution were quantitatively analyzed, and a model was developed that can be used to accurately predict the fuel distribution of the port-injected fuel at different operating conditions with an average estimation error of 1.5% in cylinder-specific fuel flow. A model-based control strategy is implemented to adjust the fueling at each port and shown to significantly reduce the cylinder-to-cylinder variations in fuel distribution.

Safe operation of dual-fuel engines using constrained stochastic control

“…60 Additionally, multicylinder engines might present uneven fuel distribution from the PFI system, direct injectors ageing, or EGR dispersion between cylinders when using high pressure EGR conditions. 61,62 Henceforth, the resonance intensity of a given operating condition can be understood as a stochastic phenomena, in the same way than knock is understood in spark ignited engines.…”

Dual-Fuel Combustion

“…While RCCI methods are promising, these modes suffer from several technical challenges. First, cycle-to-cycle and cylinder-to-cylinder variations can be more dramatic than in conventional diesel combustion [62,63]. Since fuel and air mixing are critical and high amounts of recirculated exhaust gas are typically leveraged in these modes, small variations in the in-cylinder fuel quantities and gas mixture can lead to significant variations in the combustion process.…”

“…Since fuel and air mixing are critical and high amounts of recirculated exhaust gas are typically leveraged in these modes, small variations in the in-cylinder fuel quantities and gas mixture can lead to significant variations in the combustion process. Combating such variations is likely to require more complex control strategies and additional engine sensors [62].…”

Instantaneous and cycle optimization of fuel usage on a dual fuel vehicle leveraging gasoline and natural gas

“…34 Efforts on dual fuel CI engines, using fuels such as natural gas and diesel, have used linearized models along with PI controllers to control the timing of combustion and the pressure rise rate, 35 and even leveraged openloop control approaches. 36 More complex strategies including feedback and feedforward controllers have also been implemented to control combustion phasing on a dual fuel RCCI engine by Arora and Shahbakhti, 37 and more specific issues such as the control of fuel distribution on dual fuel RCCI engines utilizing diesel and natural gas have been studied in Kassa et al 38 While these prior dual fuel control efforts have focused on algorithms that are suitable for a variety of engine platforms and advanced combustion modes, they do not address the use of a CNG and gasoline dual fuel SI engine operating with a conventional combustion strategy. In contrast, the algorithm considered here seeks to utilize two fuels on a stock spark-ignited engine, and is easy adaptable for production vehicles.…”

“…34 Efforts on dual fuel CI engines, using fuels such as natural gas and diesel, have used linearized models along with PI controllers to control the timing of combustion and the pressure rise rate, 35 and even leveraged open-loop control approaches. 36 More complex strategies including feedback and feedforward controllers have also been implemented to control combustion phasing on a dual fuel RCCI engine by Arora and Shahbakhti, 37 and more specific issues such as the control of fuel distribution on dual fuel RCCI engines utilizing diesel and natural gas have been studied in Kassa et al 38…”