Evaluation of the environmental and financial impacts of faults in bus pneumatic systems

Abstract

In recent years, a push towards a cleaner transport sector has been given importance, with various regulations helping to achieve this goal. One of the major culprits of emissions in this sector are heavy vehicles, such as buses, which even though in minority, account for 27 per cent of all emissions. These types of vehicles make use of compressed air in the Bus Pneumatic System (BPS) to power auxiliaries, mainly the brakes, suspension and doors. From a review and problem analysis which was carried out in this study, these systems can be quite inefficient due to leakages and faults. Maintenance of BPSs is also often overlooked due to its effect on vehicle downtime. To address this problem, monitoring systems have recently started to be developed. Nevertheless, such systems are still limited and knowledge in this area is quite scarce.

Indeed, in order to better comprehend how a typical BPS operates, tests on an actual vehicle were performed during the study. It was concluded that to power the pneumatic auxiliaries, 4.4 per cent of the vehicle’s total fuel is required. The next step was to understand how different factors, both operational and fault oriented, affect the system, whilst also finding factors which help in identifying and quantifying faults. This was possible by performing tests on a set-up designed to depict and monitor a typical BPS, containing the air suspension and pneumatic cylinder, both used frequently during bus use, where the pressure, flow rate and cycle time would be observed.

The results showed that a system leak and a faulty double acting actuator increased the volume of compressed air, whilst the cycle time was only affected when the faulty cylinder was induced. To find more parameters which help in identifying fault sources, the pressure standard deviation within each stop was analysed, where for both the leak and the faulty cylinder, a considerable decrease, i.e. 16 and 6 per cent, respectively, was recorded, as compared to the control. In addition it was concluded that the end effectors should not be actuated separately, since the test time was increased by 20 per cent. Furthermore, the real life repercussions of faults were also investigated, with the main outcomes being that in order to offset the annual emissions imposed by the leak per vehicle, 7 household solar panels would be required, thereby increasing the pneumatic fuel percentage to 5.6 per cent.