This paper presents a novel approach to augment existing engine calibrations to deliver improved engine performance during a transient, through the application of multi-objective optimization techniques to the calibration of the Variable Valve Timing (VVT) system of a 1.0 litre gasoline engine. Current mature calibration approaches for the VVT system are predominantly based on steady state techniques which fail to consider the engine dynamic behaviour in real world driving, which is heavily transient.In this study the total integrated fuel consumption and engine-out NOx emissions over a 2-minute segment of the transient Worldwide Light-duty Test Cycle are minimised in a constrained multiobjective optimisation framework to achieve an updated calibration for the VVT control. The cycle segment was identified as an area with high NOx emissions. The optimisation framework was developed around a Mean Value Engine Model (MVEM) with representative engine controls which was validated against an engine tested on a dynamometer. The aim of this study was to demonstrate a practical benefit without having to significantly change the existing engine control strategy. Offline optimization with the MVEM model allows exploitation of workstation computational performance to effectively explore the calibration space, reducing both time and investment in engine testing.The initial simulation optimization results show a strong dominance of both fuel and NOx objectives with a potential reduction in fuel consumption and engine out NOX emissions of up to 5% and 18% respectively compared to the original steady-state based VVT calibration. Engine experimental results have confirmed that NOX emissions can be significantly reduced without any significant detriment to fuel economy over this 2min transient.
This paper documents an investigation into the performance and thermal efficiency of an air-cycle Environmental Control System (ECS) artificially injected with common operational failure modes. A two-wheel bootstrap system is taken from an in-service military fast-jet and installed in a bespoke Ground Test Facility (GTF) at the ECS Research Facility, Loughborough University, UK. The failure modes investigated are bleed air blockages in the intercooler and in the low-pressure water extractor, as well as positional inaccuracy in cycle bypass control valves. The full range of degradation in each fault is considered, allowing the quantification of overall system performance degradation. The performance of the system is found to be insensitive to moderate bleed air blockages (up to 80% by pipe cross-section area), whilst blockages at low pressure are more detrimental to cycle performance than blockages at high pressure. The cycle and/or control system will self-regulate around most degrading-type faults. This particular system is most sensitive to a failure at one bypass valve, where the hardware allows partial redundancy of the valve but the control system does not.
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