Boeing 737-400 Passenger Air Conditioner Control System Model for Accurate Fault Simulation

Abstract

This paper is a continuation of the authors' work on the development of a systematically derived PACK simulation for accurate fault diagnostics, utilising a model-based approach. In practise the PACK simulation accuracy is dependent on a number of factors, which include the understanding of its control system. This paper addresses this by taking an in-depth look at the factors controlling the operation of the PACK in order to enable the gap between the theoretical understanding of the PACK and the engineering design of the system to be bridged, and accurate simulations under healthy and degraded scenarios obtained. The paper provides a comprehensive explanation of the PACK control system elements (principally valves) and verifies their operation based on experimental test data acquired from a B737-400 aircraft. A discussion of the control used in the simulation is then given, resulting in the correct temperature, pressure and flow being delivered to the cabin. The overall simulation results are then presented to demonstrate the importance of employing a systematically derived control logic. They are then further used to assess the impact of degradation in the main PACK valves.

Evaluation of Component Level Degradation in the Boeing 737-800 Air Cycle Machine

“…The mixing of TCV air is controlled to match the PACK outlet temperature against the cabin demand. In references [8,9] authors have thoroughly reported the functionality of the PACK and its operation under various operating modes, including the control system. The focus of this paper is on the ACM functionality and evaluation of its degradation at the component level.…”

“…Based on the the findings conceived from the evaluation of degradation in the PACK primary heat exchanger, secondary heat exchanger, ram inlet, TCV, and PV reported by the authors in [8,9], and with the results reported herein for the ACM. The formulation of arobust PACK system-level diagnostics can be implemented to formulate a through-life maintenance approach for the PACK, like the one demonstrated by the authors in Ref.…”

“…To understand the failure mechanisms and fault modes associated with the PACK at subsystem and component level, the athors have reported in [8,9] the evaluation of degradation in the PACK heat exchangers, ram air system, flow and temperature control valves, and the development of associated fault diagnostics [10]. In this paper, a further expansion of the research to investigate critical faults associated with the PACK ACM has been carried out.…”

Development of a Novel Ground Test Facility for Aircraft Environmental Control System

“…The cabin temperature demand can be regulated through the input dials mounted on the P5 overhead panel within the cockpit [21]. On the B737-400 aircraft, the cabin temperature demand can be regulated within the range of 18C to 30C.…”

“…and will only open once the initial control loop between the PACK controller and the WS o sensor is completed [21]. As shown in Figure 9(b), when the PACK is switched on, the measured pTCV mass flow peaks and then gradually reduces.…”