Sick of smelly air travel?

Research in focus March 2013

Just about everyone who has ever travelled has experienced unpleasant odors on airplanes. The worst-case scenario may look like this: you have just settled in to your seat when you’re suddenly overwhelmed with the strong smell of another passenger’s perfume combined with the stench of the washrooms a few rows ahead. Passengers may cope with this attack on the olfactory nerves by briefly holding their breath and hoping that the aircraft’s air ventilation system quickly kicks in. During the flight, the smell of food and human perspiration is added to the mix. “It doesn’t have to be this way,” says Dr. Andrea Burdack-Freitag, a scientist in the working group for sensory at the Fraunhofer Institute for Building Physics IBP. Together with her research partners, she has declared war on unpleasant odors in airplanes. The project is part of a broader initiative sponsored by Germany’s Federal Ministry of Economics and Technology (BMWi.)

For the time being, the air supply for passengers and crewmembers on airplanes is the result of a compromise that combines a heated, energy-intensive supply of fresh air with energy-saving air recirculation. This system is used to limit what are known as peaks in unbearable smells. However, until now there has been no technical solution that responds directly and flexibly to individual smells. With the current system, the level of fresh air supply is too high in situations where smells are only a minor issue, which means energy is wasted heating outside air unnecessarily.

The “Systems and technologies for energy management in performance-enhanced aircraft architectures” (STELLA) project receives 934,000 euros in support from the BMWi as part of its Aeronautical Research Program IV. The project participants hope to gain a better understanding of energy flows in the pressurized fuselage, and they aim to use the findings of their research to optimize energy management and improve air quality in airplane cabins. Besides Fraunhofer IBP, there are several other organizations taking part in the project: the EADS Sensors, Electronics & Systems Integration department, RWTH Aachen (E.ON Energy Research Center), and AppliedSensor GmbH, a manufacturer of air-quality sensors for the operation of ventilation systems.
Over the course of the research project, several air-quality sensors were tested at a Flight Test Facility (FTF) located on the premises of Fraunhofer IBP in Holzkirchen, Germany. The tests were carried out both under defined conditions in the lab and on test subjects in real flight conditions. During a simulated medium-haul flight with passengers, a range of sensors were tested under real cabin conditions: humidity and air pressure were relatively low, and temperatures were constant. Sensor signals were recorded at different points in the flight, and the test subjects were asked to evaluate air quality in the cabin. The sensors used during the test flight were configured by the researchers in the lab beforehand. They also tested the sensors to make sure that they were well suited to the substances that typically contaminate the air. “We used IR sensors for the tests that record carbon dioxide, nitrous oxide and ozone levels. We also applied metal-oxide semiconductors that react to anthropogenic emissions such as breath, flatulence, or the consumption of food and drink,” says Burdack-Freitag.
In so doing, the scientists divided the flight into typical phases and induced specific odors in each phase. First, the test subjects boarded the empty plane and experienced the simulated climbing and cruising phase (without activity). They were then served lunch with odor-intensive drinks (wine and beer) as well as coffee. Next, they went through the descent phase and exited the aircraft. During each phase, the test subjects evaluated the intensity of odors using a pre-defined smell intensity scale. The passengers did not arrive for the flight unprepared: they had already been familiarized with the intensity values beforehand. With a special device, they were able to “sniff out” a good indication of their impressions, which could then be used to assess the intensity of smells in the cabin. “We developed this device at Fraunhofer IBP especially for the test subjects’ sensory training. It meets the norms for the assessment of air quality,” says Burdack-Freitag. The smell intensity scale measures values between 0 and 16 π, with 8 π corresponding to slightly stale office air. In addition, the hedonics of each phase were assessed, meaning the degree to which the test subjects considered smells to be pleasant or unpleasant.
“The test showed that the sensor signals and the test subjects’ evaluations were clearly correlated,” says Burdack-Freitag. The phases with the most intensive smells were, as expected, meal times as well as the phase during which coffee was served. These events were also clearly reflected in the sensor signals. This shows that the sensors are well suited to recording and transmitting the specific occurrence of smells. This, in turn, could make it possible for ventilation systems to respond immediately when smells reach their peak. The STELLA project will continue until September 2013. And while it will take some time until intelligent ventilation systems are ready for market, at least airline passengers have the comfort of knowing that smelly travel will one day be a thing of the past.

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