Raising the Green Bar
By Andy Bateman
Pratt & Whitney Canada's commitment to the future.
By Andy Bateman
Advanced engine design and manufacturing, and a $1.5-billion research and development program, underscore Pratt & Whitney Canada’s ongoing commitment to technology.
With the current focus on climate change and the environment, many companies are hastily reinventing themselves to go green while others are already there. P&WC certainly belongs in the latter category, with the development and implementation of green technology an established part of doing business. Going forward, P&WC’s five-year R&D program promises to raise the green bar further still. The program will develop new engine and fuel technologies for the next generation of aircraft and includes a $75-million investment in over 600 collaboration projects, working with the National Research Council and 20 Canadian universities.
Vice-president of engineering Walter Di Bartolomeo explains that the two main aims of P&WC’s green technology developments are maximizing customer value and minimizing environmental impact. These goals are not achieved overnight, with the development of the company’s Talon 2 combustion technology, for instance, taking several years. One of Talon 2’s main goals has been to reduce emissions of nitrogen oxides (NOx). This goal was achieved through a detailed understanding of the combustion process and optimum burn parameters such as fuel/air mixture and burn location. The result is a lean fuel mixture burning at the optimum temperature distribution to provide complete combustion. As is often the case, green developments also make good business sense. The PW307 engine which recently entered service on Dassault Aviation’s Falcon 7X has excellent fuel efficiency; NOx emissions are 33% lower than current International Civil Aviation Organization (ICAO) standards and also meet Zurich 5 emissions requirements for landing fee surcharges.
Di Bartolomeo adds that Talon 2 technology is part of an evolutionary process, with P&WC now testing Talon 3 as part of a new 10,000-pound thrust class engine. This new engine is being developed for the next generation of long-range corporate jets and will reportedly surpass current ICAO standards by over 35% for carbon monoxide and by more than 50% for nitrogen oxides, unburned hydrocarbon and smoke emissions.
Environmental initiatives have also been successful in significantly reducing engine noise, an issue of particular interest to those under busy flight paths. One research program identified rotating parts, the combustion process and exhaust as the main components of engine noise, with each source tackled individually. On P&WC’s new 10,000-pound thrust class engine, noise levels have been reduced by at least 20 EPNdB (the units of Effective Perceived Noise Level used to measure aircraft noise) below the latest ICAO Stage IV requirements, with this significant reduction achieved by detailed analysis of the engine’s physics. On the cold side, as an example, new acoustic liners have reduced turbofan-generated noise, while an advanced mixer on the hot side reduces noise by blending a cold air stream into the hot jet stream.
Company literature indicates that engine fuel efficiency is being improved by the development of improved engine components and lighter materials. Di Bartolomeo gives two examples: “Innovations such as single crystal turbine blades allow higher operating temperatures which in turn deliver improved combustion and fuel efficiency. At the same time, the use of different materials such as nickel alloys and composite materials help to reduce weight and thereby improve the power-to-weight ratio of an engine.” P&WC’s next-generation engines are being designed to deliver a five- to seven-percent improvement in fuel efficiency. This, combined with advances in aircraft design and technologies, will further contribute to the “greening” of this industry.
P&WC also reports that research and development work has resulted in the elimination of materials of concern in its newest engine models and generated significant improvements in waste, air emissions, and water and energy consumption in both the engine manufacturing and repair processes. Two more examples from Di Bartolomeo: “Cadmium has historically been used to provide corrosion protection. In recent years, the development of new paint technology has enabled cadmium use to be cut by 90% and the company’s goal is to eliminate its use entirely. We have also eliminated the use of varsol-based solvents as cleaning agents during engine manufacture, by developing a water-based cleaner.’’
With the performance and emissions of engines so closely related to the quality and quantity of fuel burned, it is no surprise that P&WC’s research and development program includes the use of alternative fuels such as hydrogen and biofuels. P&WC recently announced that the company’s PW308 engine will power the White Knight II (WK2), Virgin Galactic’s Suborbital Spaceship Launcher. As part of this project, P&WC will team up with owner The Spaceship Company (TSC) and Virgin Fuels to evaluate the use of advanced biofuels in White Knight II. Di Bartolomeo does not see major technological barriers to using these fuels, but their availability or lack thereof could be an issue. “Tests have shown that our existing engines are relatively forgiving and perform well with different fuels and we believe that biofuels can be burned successfully with appropriate engine optimization and some relatively minor modifications. However, ensuring a reliable supply in the necessary quantities could be the bigger challenge.”
A closer look at the company’s PW300 engine series reveals some of the developments incorporated into current engine design. Company literature describes the PW300 engines as advanced, high bypass ratio turbofan engines in the 4,500 lbs to 8,000 lbs thrust range, designed for clean, quiet, efficient and low-cost operation. Main features of the PW300 series include a foreign object damage resistant wide chord fan designed to the latest 3D aero modeling techniques to optimize fuel burn. The engines’ high pressure compressor is a four-stage axial configuration (the first two stages having variable geometry guide vanes) comprised of integrally bladed rotor plus a one-stage centrifugal impeller manufactured from advanced titanium alloys for weight and durability advantages. Through flow combustors ensure efficient clean combustion to meet the latest NOx emission requirements. The high-pressure turbine module is a two-stage configuration with cooled vanes and first-stage blades; advanced alloys coupled with proven cooling technology results in low maintenance and direct operating cost through increased durability. The low-pressure turbine is a three-stage module uncooled and moderately loaded for good cyclic life and low exhaust losses. A forced exhaust mixer on the PW306, PW307, and PW308 engines provides improved fuel burn advantage with a resultant noise signature inside US Federal Aviation Regulations (FAR) Stage-3 requirements. Thrust management is governed by a Full Authority Digital Electronic Control (FADEC) for reduced pilot workload, enhanced engine protection and diagnostic capability.
P&WC has over 7,000 employees in Canada. Production facilities are located
in Longueuil, Que., Mississauga, Ont., Lethbridge, Alta. and Halifax. Longueuil and Mississauga are the main centres for research and development. P&WC is a subsidiary of United Technologies Corporation, a high-technology company based in Hartford, Conn.
In a recent interview, Walter Di Bartolomeo, Vice-president of engineering for Pratt & Whitney Canada, commented that the use of biofuels for aviation was technically feasible but added that the availability of such fuels could be an issue.
Di Bartolomeo is in good company, as this view is echoed by the European Commission Directorate-General For Energy And Transport in its current project entitled Feasibility study on the use of renewable energy sources, in particular biofuels for aviation. In the project tender documents, the commission states that “it is imperative to have secure, environmentally friendly and affordable supplies of energy that can be used in a sustainable way.” It adds: “The most promising biofuels, in terms of security of supply and environmental benefits in the short/medium term should be selected for further study.”
The commission defines biofuels as either first-generation biofuels (bioethanol from sugar-based crops or starch and biodiesel from seeds, used cooking oil and animal tallow) or second-generation biofuels (synthetic biofuels via the gasification route and the production of synthesis gas followed by catalytic conversion), bioethanol from lignocellulosics) or hydrogenated oils and fats.
SIDEBAR: JET ENGINE EMISSIONS
Jet aircraft engines emit water vapour, carbon dioxide (CO2), small amounts of nitrogen oxides (NOx), hydrocarbons, carbon monoxide and sulphur gases formed by the high-temperature combustion of jet fuel during flight. The quantities of nitrogen oxides and carbon monoxide emitted during combustion are a function of the efficiency of the combustion process and properties of the fuel burned, while emissions of carbon dioxide and water vapour are a function of the amount of fuel burned. Clearly, R&D aimed at combustion and fuel efficiency is instrumental in ensuring a green aerospace industry.
The burning of fossil fuels and consequent release of carbon dioxide into the atmosphere is believed to be a key factor in global climate change. Aviation’s overall potential for influencing climate has been recently assessed to be about 3.5 percent of the potential from all human activities, and annual global consumption of jet fuel is estimated to be at least 200 million tonnes. During the process of burning this fuel, over 600 million tonnes of carbon dioxide are released into the atmosphere. Put another way, if all the jet engines currently operating achieved a one-percent improvement in fuel efficiency, annual global carbon dioxide emissions would be reduced by six million tonnes.
Nitrogen oxides (NOx) include the gases nitrogen oxide (NO) and nitrogen dioxide (NO2). NOx is formed primarily from the liberation of nitrogen contained in fuel and nitrogen contained in combustion air during combustion processes. NO emitted during combustion quickly oxidizes to NO2 in the atmosphere. NO2 dissolves in water vapour in the air to form acids, and interacts with other gases and particles in the air to form particles known as nitrates and other products that may impact the environment. NO2 is one of the two primary contributing pollutants, along with volatile organic compounds (VOCs) to the formation of ground-level ozone. NOx emissions are a precursor to the formation of ground-level ozone, also known as smog. Also, NOx reacts in the atmosphere to form secondary particulate matter (PM2.5). In addition, NOx, ozone, and PM adversely affect the environment in various ways including visibility impairment, crop damage and acid rain.
Exhaust contrails are line-shaped clouds sometimes produced by aircraft engine exhaust, typically at altitudes of 26,000 feet or higher where the air temperature is below –40 Celsius. Composed primarily of water in the form of ice crystals, contrails do not pose health risks to humans. Contrails do affect the cloudiness of the Earth’s atmosphere and therefore might affect atmospheric temperature and climate. The overall impact of contrails on climate is controversial, but there is no doubt that in any particular application, a fuel efficient engine will burn less fuel to do the same amount of work and in doing so generate less water vapour.