COSMOS: Device burns fuel with almost zero emissions

As an intern at COSMOS Online:

A device has been designed to burn natural gas fuel with next to no emission of nitrogen oxides (NOx) and carbon monoxide (CO), which are two of the primary causes of air pollution.

The combustor, called the Stagnation Point Reverse Flow Combustor, significantly reduces NOx and CO emissions in a variety of aircraft engines and gas turbines that burn gaseous or liquid fuels. It burns fuel with NOx emissions below 1 parts per million (ppm) and CO emissions lower than 10 ppm, significantly lower than emissions produced by other combustors.

Attaining ultra low emissions has become a top priority for combustion researchers as U.S. federal and state restrictions on pollution continuously reduce the allowable levels of NOx and CO produced by engines, power plants and industrial processes.

"We must burn fuel to power aircrafts and generate electricity for our homes. The combustion community is working very hard to find ways to burn the fuel completely and derive all of its energy while minimising emissions," said Ben Zinn, a key collaborator on the project at the Georgia University of Technology, USA. "Our combustor has an unbelievably simple design, and it would be inexpensive to make and inexpensive to maintain."

The combustor burns fuel in low temperature reactions that occur over a large portion of the combustor. By eliminating all high temperature pockets through better control of the flow of the reactants and combustion products within the combustor, the device produces far lower levels of NOx and CO and avoids acoustic instabilities that are a problem in current low-emissions combustors.

Existing low-emission combustors premix fuel with a large amount of swirling air flow prior to injection into the combustor. This requires complex and expensive designs, and the combustion process often excites instabilities that damage the system.

The Stagnation Point Reverse Flow Combustor eliminates the complexity associated with premixing the fuel and air by injecting the fuel and air separately into the combustor while its shape forces them to mix with one another and with combustion products before ignition occurs.

The combustor was originally designed for NASA, for use in aircraft engines and power-generating gas turbines that must stably burn large amounts of fuel in a small volume over a wide range of power settings (or fuel flow rates). But the design can be adapted for use in a variety of applications, including something as large as a power generating gas turbine or as small as a water heater in a home. Current research is addressing issues that may arise from varying design parameters, such as combustor geometry, fuel, or inlet and operating pressure.

"We wanted to have all the clean-burning advantages of a low temperature combustion process while burning a large amount of fuel in a small volume," Zinn said.

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Mars Youth: Searching for life on other planets

As a student at St Hildas Anglican School for Girls and a member of the Mars Society Youth Chapter:

For centuries mankind has been scouring the skies in search of extraterrestrial life. But what is “life”? How do we know when we have found it? The Oxford Dictionary defines life as the “capacity for growth, functional activity, and continuous change until death”. But scientists fear that similar criteria for identifying life may not apply on other planets.

The first sign of life elsewhere will probably not be as obvious as little green men or purple eighty-legged animals. In fact, it is likely to be microscopic and maybe not at all similar to life on Earth. So, where and how should we search?

Criteria for Life

Before we begin our search, we have to work out what it is exactly that we are searching for. The first criterion for life (as we know it) is energy. Life requires energy to perform life-sustaining processes such as respiration. This energy can be in practically any form - geothermal heat, tidal energy, chemical energy, or sunlight. This does not appreciably narrow down the places where we should look.

The National Aeronautics and Space Administration (NASA) believes that the secret to life is liquid water, which translates into location. “Life cannot survive in hot conditions like on our sun. Life needs to be where it is not too hot and not too cold, and at a temperature at which liquid water can exist.” Thus, it is important to pay special attention to places which can support liquid water, either at the surface or subsurface of the celestial body.

The chemicals present in the atmosphere of a planet or a moon are important indicators of the presence of life. As per James Lovelock’s Gaia hypothesis, on any planet with thriving life, that life will have control over the atmospheric composition. This is because life will alter its surroundings in order to optimize them. For Earth-like life, this optimization takes the atmosphere far from the equilibrium state to a composition which cannot be achieved without the presence of life. Therefore, certain ratios of carbon dioxide, water vapor, and oxygen in the atmosphere are possible indicators that the astral body hosts life. While finding a non-equilibrium atmosphere is a sure sign of life, this is not a necessary condition. Oxygen appeared on Earth only about 500 million years ago, but we know that a whole world of bacteria thrived long before that, and life originated over 3.5 billion years ago.

Location, location, location

At 149.6 million kilometres from the Sun, Earth is pretty much in the perfect spot. As a result of its location and its significant greenhouse effect (CO 2 and water vapour in the atmosphere), Earth maintains an average temperature of 15 degrees Celsius – an ideal temperature for life to thrive.

Mars is the second most favourable place for life, and human habitation. This is due to its relative similarity to Earth – both are solid planets and are within the range of distances from the Sun which allow for liquid water conditions (the habitable zone). Similar to Earth, Mars also contains the elements required for Earth-like life - C, H, N, O, P, S, and water. Currently, Mars is too cold and has too thin an atmosphere to support liquid water on its surface or in the near subsurface. However, Mars is believed to have been very much like the Earth when the planets formed - and life on Earth arose. The reason behind the significant differences between the two planets today is thought to be Mars’ lack of plate tectonics. The carbon dioxide responsible for the greenhouse warming would have reacted with water to form carbonate rocks, but could not be recycled back into the atmosphere; therefore, Mars could not maintain a significant greenhouse warming.

Other celestial bodies with good prospects of hosting life (as we know it) include four of Jupiter’s moons - Europa, Enceladus, Titan and Io.

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