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Viewing 1 to 30 of 4509
2017-09-19
Technical Paper
2017-01-2026
Narayanan Komerath, Shravan Hariharan, Dhwanil Shukla, Sahaj Patel, Vishnu Rajendran, Emily Hale
Abstract Our concept studies indicate that a set of reflectors floated in the upper atmosphere can efficiently reduce radiant forcing into the atmosphere. The cost of reducing the radiant forcing sufficiently to reverse the current rate of Global Warming, is well within reach of global financial resources. This paper summarizes the overall concept and focuses on one of the reflector concepts, the Flying Carpet. The basic element of this reflector array is a rigidized reflector sheet towed behind and above a solar-powered, distributed electric-propelled flying wing. The vehicle rises above 30,480 m (100,000 ft) in the daytime by solar power. At night, the very low wing loading of the sheets enables the system to stay well above the controlled airspace ceiling of 18,288 m (60,000 ft). The concept study results are summarized before going into technical issues in implementation. Flag instability is studied in initial wind tunnel experiments.
2017-09-19
Technical Paper
2017-01-2141
Fengmei Li, Peng Ke
Abstract For the ice protection of the engine air induction part manufactured with low thermal conductivity composite material, the combined heating method using interior impingement and exterior air film has certain advantages. To study the influence of the external jet air film on the impingement characteristics of droplets, the numerical simulation method of three dimensional water droplet impingement based on Eulerian method was developed and verified by experimental data from references. The droplets impingement characteristics under three different blowing ratios and two different velocities were then investigated based on the configuration of 3D cylinder with two parallel jet holes.
2017-09-19
Technical Paper
2017-01-2143
Narayanan Komerath, Dhwanil Shukla, Shravan Hariharan, Sahaj Patel, Nandeesh Hiremath
Abstract A direct solution to Global Warming would be to reflect a part of sunlight back into Space. A system tradeoff study is being developed with three of the concepts that are being evaluated as long-endurance high-altitude reflectors. The first concept is a high aspect ratio solar powered flying wing towing reflector sheets. This concept is named “Flying Carpet”. Second is a centrifugally stretched high altitude solar reflector (CSHASR). The CSHASR has 4 rotors made of reflector sheets with a hub stretching to 60 percent of the radius, held together by an ultralight quad-rotor structure. Each rotor is powered by a solar-electric motor. A variation on this concept, forced by nighttime descent rate concerns, is powered by tip-mounted solar panels and propellers with some battery storage augmenting rotational inertia as well as energy storage. The third concept is an Aerostatically Balanced Reflector (ABR) sheet, held up by hydrogen balloons.
2017-09-19
Technical Paper
2017-01-2123
Violet Leavers
Abstract The need to maintain aircraft in remote, harsh environments poses significant challenges. For example, in desert assignments or on-board carrier vessels where frequent rotation of staff with variable levels of skill and experience requires condition monitoring equipment that is not only robust and portable but also user friendly and requiring a minimum of training and skill to set up and use correctly. The mainstays of any on-site aircraft maintenance program are various fluid and particulate condition monitoring tests that convey information about the current mechanical state of the system. In the front line of these is the collection and analysis of wear debris particles retrieved from a component’s lubricating or power transmission fluid or from magnetic plugs. It is standard practice within the specialist laboratory environment to view and image wear debris using a microscope.
2017-09-19
Technical Paper
2017-01-2124
Violet Leavers
Abstract Within the aviation industry analysis of wear debris particles recovered from magnetic plugs and lubricating fluids is an essential condition monitoring tool. However, in large organisations, high staff turnover in remote work environments often leaves dangerous gaps in on-site support and background knowledge. The current work develops interactive software for wear debris particle classification, root cause diagnosis and serviceability prognostics. During the research several hundred wear debris particle images were collected, analysed and classified by a number of experts. At each stage of the analysis the experts were questioned about the knowledge and experience used to make their diagnoses and prognoses. The end result is an extensive knowledge base representing the combined expertise of a number of highly trained engineers, each with decades of hands-on experience.
2017-06-26
White Paper
WP-0001
NASA has embarked on an ambitious program to integrate additive manufacturing techniques and to develop processes for the microgravity environment. The most recent example of this program is the successful launch and deployment of the first 3D printer on the International Space Station. In this one-year effort, students were required to meet a series of milestones to design, manufacture, and test their ideas in close cooperation with members of the NASA Exploration Augmentation Module (EAM) concept team.The participants in this project were tasked with thinking of new solutions using AM that would simultaneously be recyclable with minimal loss in mechanical properties but also have the capacity for high mechanical properties. Working in interdisciplinary teams, the participant teams investigated the use of recycled materials, characterization, testing, modeling, and tool development.
2016-09-20
Technical Paper
2016-01-2004
M. Parvez Alam, Dinesh Manoharan
In this paper we discuss about the design and development of an “Autonomous Amphibious Unmanned Aerial Vehicle (AAUAV)” that can fly autonomously to the polluted water areas where human accessibility is formidable to test the water quality. The AAUAV system is an integrated multi-copter with tilt rotor capability to facilitate easy landing, navigation and maneuver on water. A 3D CAD model has been designed and analyzed. A specific propulsion system has been devised and lab tested. A proof of concept model has been made and tested in the field with its instruments to ascertain its technical/ operational feasibility. This system can also be tailored to collect and store the water samples from the polluted sites for further comprehensive research at the laboratory. AAUAV system is the novel solution to the polluted environment through a complete integrated system. This will be an effective alternative for the conventional water sampling techniques.
2016-09-20
Journal Article
2016-01-2022
Ajay Rao, Vivek Karan, Pradeep Kumar
Abstract Turbulence is by far the number one concern of anxious passengers and a cause for airline injuries. Apart from causing discomfort to passengers, it also results in unplanned downtime of aircrafts. Currently the Air Traffic Control (ATC) and the meteorological weather charts aid the pilot in devising flight paths that avoid turbulent regions. Even with such tailored flight paths, pilots report constant encounters with turbulence. The probability of turbulence avoidance can be increased by the use of predictive models on historical and transactional data. This paper proposes the use of predictive analytics on meteorological data over the geographical area where the aircraft is intended to fly. The weather predictions are then relayed to the cloud server which can be accessed by the aircraft planned to fly in the same region. Predictive algorithms that use Time series forecasting models are discussed and their comparative performance is documented.
2016-04-05
Technical Paper
2016-01-0212
Paras Kaushal, Satishchandra C. Wani
Abstract TeamIndus is the only Indian participant in the Google Lunar X Prize (GLXP). GLXP, also referred to as Moon 2.0, is an inducement prize space competition organized by the X Prize Foundation, and sponsored by Google. The mission objective is to soft land a rover on moon, travel 500 meters and transmit HD videos and images to Earth. Team Indus’s strategy is to design and realize a lunar lander that will deliver a rover on to the surface of the moon which will accomplish GLXP mission objectives. The mission configuration comprises of four phases- Earth orbits, moon orbits, descent and surface operations. The lander during its interplanetary journey from earth to moon is exposed to different thermal loads viz. solar load, earth IR and albedo, moon IR and albedo, cold space at 4K and eclipse periods. The lander is also exposed to high temperatures of thruster nozzle during orbital transfer maneuvers.
2015-09-15
Journal Article
2015-01-2538
Yixiang Lim, Alessandro Gardi, Roberto Sabatini
Abstract Contrails and aircraft-induced cirrus clouds are reputed being the largest components of aviation-induced global warming, even greater than carbon dioxide (CO2) exhaust emissions by aircraft. This article presents a contrail model algorithm specifically developed to be integrated within a multi-objective flight trajectory optimization software framework. The purpose of the algorithm is to supply to the optimizer a measure of the estimated radiative forcing from the contrails generated by the aircraft while flying a specific trajectory. In order to determine the precise measure, a comprehensive model is employed exploiting the Schmidt-Appleman criterion and ice-supersaturation regions. Additional parameters such as the solar zenith angle, contrail lifetime and spread are also considered.
2015-09-15
Technical Paper
2015-01-2419
Naoki Seki, Noriko Morioka, Hidefumi Saito, Hitoshi Oyori
Abstract This paper describes the concept of an air/fuel integrated thermal management system, which employs the VCS (Vapor Cycle System) for the refrigeration unit of the ECS (Environment Control System), while exchanging the heat between the VCS refrigerant and the fuel into the engine, and presents a feasibility study to apply the concept to the future all electric aircraft systems. The heat generated in an aircraft is transferred to the ECS heat exchanger by the recirculation of air and exhausted into the ram air. While some aircraft employ the fluid heat transfer loop, the transferred heat is exhausted into the ram air. The usage of ram air for the cooling will increase the ram drag and the fuel consumption, thus, less usage of ram air is preferable. Another source for heat rejection is the fuel. The heat exchange with the fuel does not worsen the fuel consumption, thus, the fuel is a preferable source.
2015-09-15
Technical Paper
2015-01-2413
Anngwo Wang, Jonathan Davies, Seth Gitnes, Lotfi El-Bayoumy
Abstract The instantaneous efficiency of an epicyclic geared rotary actuator is an important factor in sizing flight control systems where compound epicyclic gear trains are typically used. The efficiency variation can be smooth or fluctuating depending on the combination and timing of the teeth of ring gears, planet gears and sun gears. In a previous paper [1], the instantaneous efficiency characteristics of actuators with symmetric planets were investigated. The actuator's reacting forces on the planets are symmetric and the overall length of the planet gears will not affect the efficiency. In this paper, a cantilever actuator with asymmetric planet gears is studied. The length and location of the reaction forces on the planet gears are key factors in the efficiency calculation. Theoretical derivation is presented and test results are compared.
2015-09-15
Technical Paper
2015-01-2469
Reece Clothier, Brendan Williams, Achim Washington
Abstract One of the primary hazards associated with the operation of Unmanned Aircraft (UA) is the controlled or uncontrolled impact of the UA with terrain or objects on the terrain (e.g., people or structures). National Aviation Authorities (NAAs) have the responsibility of ensuring that the risks associated with this hazard are managed to an acceptable level. The NAA can mandate a range of technical (e.g., design standards) and operational (e.g., restrictions on flight) regulatory requirements. However, work to develop these regulations for UA is ongoing. Underpinning this rule-making process is a safety case showing how the regulatory requirements put in place ensure that the UA operation is acceptably safe for the given application and environment.
2015-09-15
Technical Paper
2015-01-2474
Christopher W. Lum, Alexander Summers, Brian Carpenter, Angel Rodriguez, Matthew Dunbabin
Abstract In many parts of the world, uncontrolled fires in sparsely populated areas are a major concern as they can quickly grow into large and destructive conflagrations in short time spans. Detecting these fires has traditionally been a job for trained humans on the ground, or in the air. In many cases, these manned solutions are simply not able to survey the amount of area necessary to maintain sufficient vigilance and coverage. This paper investigates the use of unmanned aerial systems (UAS) for automated wildfire detection. The proposed system uses low-cost, consumer-grade electronics and sensors combined with various airframes to create a system suitable for automatic detection of wildfires. The system employs automatic image processing techniques to analyze captured images and autonomously detect fire-related features such as fire lines, burnt regions, and flammable material.
2015-09-15
Technical Paper
2015-01-2395
Vikhyat Chaudhry, Ishan Mishra
Abstract This paper describes the ZENITH Nano-Satellite cum planetary atmospheric entry vehicle, called CanSat, the first Nano-Satellite project that has been developed by Delhi Technological University (Formerly Delhi College of Engineering), India. The satellite will function for monitoring the concentrations of various gases in the atmosphere. For this, the satellite consists of arduino microcontroller interfaced with the various Micro-electromechanical system (MEMS) gas sensors for measuring the concentrations of various gases such as carbon dioxide, carbon monoxide, methane, nitrous oxides, ozone, etc. The data obtained from the CanSat will be transmitted to the ground station where all the data will be stored and also the locations will be stored using GPS sensor. The academic goal of this project is to recruit students to the field of space science and technology.
2015-09-15
Technical Paper
2015-01-2400
Craig Lawson, Irfan Madani, Ravinka Seresinhe, Devaiah K. Nalianda
Abstract With the rapid growth in passenger transportation through aviation projected to continue into the future, it is incumbent on aerospace engineers to seek ways to reduce the negative impact of airliner operation on the environment. Key metrics to address include noise, fuel consumption, Carbon Dioxide and Nitrous Oxide emissions, and contrail formation. The research presented in this paper generates new aircraft trajectories to reduce these metrics, and compares them with typical scheduled airline operated flights. Results and analysis of test cases on trajectory optimization are presented using an in-house aircraft trajectory optimization framework created under the European Clean Sky Joint Technology Initiative, Systems for Green Operation Integrated Technology Demonstrator. The software tool comprises an optimizer core and relatively high fidelity models of the aircraft's flight path performance, air traffic control constraints, propulsion and other systems.
2015-09-15
Technical Paper
2015-01-2426
Anupam Kumari, Tushar Choudhary, Y Sanjay, Pilaka Murty, Mithilesh Sahu
Abstract In comparison to other thermal power cycles, gas turbine based energy conversion cycles exhibit superior thermodynamic performance as well as reduced emission. Gas turbine manufacturers and research & development (R&D) organizations are working on modification in basic gas turbine (BGT) cycle, which are intended to improve the basic gas turbine cycle thermodynamic performance and reduce emissions. The present work reports a comparison of thermodynamic performance, NOx and CO emission for basic and intercooled gas turbine (IcGT) cycles. Various cycle operating parameters such as compressor-pressure-ratio (rp,c), combustor-primary-zone-temperature, equivalence-ratio, and residence time of gas turbine based cycles has been examined. IcGT cycle exhibits higher gas turbine specific work and gas turbine efficiency in comparison to BGT cycle for the same rp,c and turbine rotor inlet temperature.
2015-09-15
Journal Article
2015-01-2562
Tak W. Chan, Wajid Chishty, Craig Davison, David Buote
Abstract This study reports gaseous and particle (ultrafine and black carbon (BC)) emissions from a turbofan engine core on standard Jet A-1 and three alternative fuels, including 100% hydrothermolysis synthetic kerosene with aromatics (CH-SKA), 50% Hydro-processed Esters and Fatty Acid paraffinic kerosene (HEFA-SPK), and 100% Fischer Tropsch (FT-SPK). Gaseous emissions from this engine for various fuels were similar but significant differences in particle emissions were observed. During the idle condition, it was observed that the non-refractory mass fraction in the emitted particles were higher than during higher engine load condition. This observation is consistent for all test fuels. The 100% CH-SKA fuel was found to have noticeable reductions in BC emissions when compared to Jet A-1 by 28-38% by different BC instruments (and 7% in refractory particle number (PN) emissions) at take-off condition.
2015-09-15
Technical Paper
2015-01-2563
Alberto Charro, Solange Baena, Joseph K-W Lam
Abstract The paper presents an extensive assessment of the hygroscopic characteristics of a number of alternative jet fuel blends. These are blended with conventional Jet A-1 to conform with current aviation standards at a 50:50 ratio by volume, except for DSHC (Direct Sugar to Hydrocarbon), which is blended at 10% DSHC and 90% Jet A-1. Given the lack of information available on the water solubility of alternative jet fuels, an effective analysis of experimental data about this characteristic in six different alternatives was performed. These included four ASTM approved alternatives (two Fischer-Tropsch (FT) synthetics from coal and natural gas, one HEFA (Hydroprocessed Esters and Fatty Acids) derived from camelina and DSHC. An extra two alternatives currently under consideration for ASTM approval were also tested; ReadiJet and an ATJ (Alcohol to Jet).
2015-09-15
Technical Paper
2015-01-2477
Alessandro Gardi, Roberto Sabatini
Abstract This paper presents the conceptual design of a new low-cost measurement system for the determination of pollutant concentrations associated with aircraft operations. The proposed system employs Light Detection and Ranging (LIDAR) and passive electro-optics equipment installed in two non-collocated components. The source component consists of a tuneable small-size and low-cost/weight LIDAR emitter, which can be installed either on airborne or ground-based autonomous vehicles, or in fixed surface installations. The sensor component includes a target surface calibrated for reflectance and passive electro-optics equipment calibrated for radiance, both installed on an adjustable support. The proposed bistatic system determines the column-averaged molecular and aerosol pollutant concentrations along the LIDAR beam by measuring the cumulative absorption and scattering phenomena along the optical slant range.
2015-09-15
Technical Paper
2015-01-2484
Michele Trancossi, Antonio Dumas, Guido Niccolai, Jose Pascoa
Abstract This paper focuses on the key problem of future aeronautics: which relates on energy efficiency and environmental footprint on a scientific point of view. Reducing emissions and increasing the energy efficiency would be both a key element to propel the market and increase the diffusion of personal aerial transport against ground transportation. Novel vehicle concepts and systems will be necessary to propel this innovation which could revolutionize our way of moving. This paper approaches an energetic preliminary design of a vehicle concept which could fulfill this social and cultural objective. Low cost energy efficient vehicles, which could be suitable for personal use with a high economic efficiency and without needs of airports, seem actually a real dream. Otherwise, is it a feasible goal or a scientific dream? Otherwise, a design method based on first and second law and thermodynamic and constructal law could allow reaching those goals.
2015-06-15
Technical Paper
2015-01-2123
Eric Defer, Jean-Louis Brenguier, Jos De Laat, Julien Delanoe, Fabien Dezitter, Michael Faivre, Amanda Gounou, Alice Grandin, Anthony Guignard, Jan Fokke Meirink, Jean-Marc Moisselin, Frederic Parol, Alain Protat, Claudine Vanbauce
Abstract The High Altitude Ice Crystals (HAIC) Sub-Project 3 (SP3) focuses on the detection of cloud regions with high ice water content (IWC) from current available remote sensing observations of space-based geostationary and low-orbit missions. The SP3 activities are aimed at supporting operationally the two up-coming HAIC flight campaigns (the first one in May 2015 in Cayenne, French Guyana; the second one in January 2016 in Darwin, Australia) and ultimately provide near real-time cloud monitoring to Air Traffic Management. More in detail the SP3 activities focus on the detection of high IWC from space-borne geostationary Meteosat daytime imagery, explore the synergy of concurrent multi-spectral multiple-technique observations from the low-orbit A-Train mission to identify specific signatures in high IWC cloud regions, and finally develop a satellite-based nowcasting tool to track and monitor convective systems over the Tropical Atlantic.
2015-06-15
Technical Paper
2015-01-2124
Amanda Gounou, Jean-Marc Moisselin, Frédéric Autones, Dominique Levaillant, Jean-Louis Brenguier, Eric Défer, Michael Faivre, Alice Grandin, Fabien Dezitter, Sandra Turner
Abstract Glaciated icing conditions potentially leading to in-service event are often encountered in the vicinity of deep convective clouds. Nowcasting of these conditions with space-borne observations would be of a great help for improving flight safety and air-traffic management but still remains challenging. In the framework of the HAIC (High Altitude Ice Crystals) project, methods to detect and track regions of high ice water content from space-based geostationary and low orbit mission are investigated. A first HAIC/HIWC field campaign has been carried out in Australia in January-March 2014 to sample meteorological conditions potentially leading to glaciated icing conditions. During the campaign, several nowcasting tools were successfully operated such as the Rapid Development Thunderstorm (RDT) product that detects the convective areas from infrared geostationary imagery.
2015-06-15
Technical Paper
2015-01-2158
Tatsuma Hyugaji, Shigeo Kimura, Haruka Endo, Mitsugu Hasegawa, Hirotaka Sakaue, Katsuaki Morita, Yoichi Yamagishi, Nadine Rehfeld, Benoit Berton, Francesc Diaz, Tarou Tanaka
Coating has been recently considered as having good potential for use in preventing in-cloud icing on the leading edge of the lifting surfaces of an aircraft in cold climates. In terms of wettability, a coat may exhibit hydrophobicity or hydrophilicity depending on its specific properties. The same applies to the ice adhesion strength, which may be either high or low. It is thus necessary to determine which type of anti-icing or de-icing coat would be appropriate for a particular application in order to fully utilize its specific properties. Notwithstanding, a coat is incapable of preventing ice accretion by itself, and a perfect icephobic coat is yet to be developed. Coating is also sometimes applied to the surfaces of electrical heaters and load-applying machines to enable them to function more effectively and use less energy. The coating used for an electric heater, for instance, should be hydrophobic because of the need for rapid removal of molten water from the surface.
2015-06-15
Technical Paper
2015-01-2115
Antonio Criscione, Suad Jakirlic, Zeljko Tukovic, Ilia Roisman, Cameron Tropea
Abstract Numerical experiments have been presently conducted aiming at studying the influence of the surface energy on the crystallization process of supercooled water in terms of the supercooling degrees. The mathematical model consists primarily of the equation governing the thermal energy field solved independently in both phases in accordance with the two-scalar approach by utilizing the Stefan condition at the interface to couple both temperature fields. The computational algorithm relying on the level-set method for solid-liquid interface capturing has been appropriately upgraded aiming at accuracy level increase with respect to the discretization of the thermal energy equation and the normal-to-interface derivative of the temperature field. The model describes the freezing mechanism under supercooled conditions, relying on the physical and mathematical description of the two-phase moving-boundary approach.
2015-06-15
Technical Paper
2015-01-2078
Alric Rothmayer, Hui Hu
Abstract A strong air/water interaction theory is used to develop a fast simplified model for the trapping of water in a film that flows over sub-grid surface roughness. The sub-grid model is used to compute correction factors that can alter mass transport within the film. The sub-grid model is integrated into a covariant film mass transport model of film flow past three-dimensional surfaces in a form that is suitable for use in aircraft icing codes. Sample calculations are presented to illustrate the application of the model.
2015-06-15
Technical Paper
2015-01-2157
Mengyao Leng, Shinan Chang, Yuanyuan Zhao
Abstract Aircraft icing causes a great threaten to flight safety. With the development of anti-icing or de-icing systems for aircraft, some attention has been paid on coating strategies for an efficient way to prevent water remaining on the surface. By application of hydrophobic or super-hydrophobic coatings, characterized by low surface adhesion, shedding of liquid from the surface can be enhanced. The motivation behind this work is to identify the way that wettability affects the motion of runback water, and establish an empirical formula of critical departure diameter. The surface property is characterized by the equilibrium contact angle and the hysteresis angle. The relationship between the air speed and the droplet shedding diameter is studied, corresponding to different surfaces.
2015-06-15
Technical Paper
2015-01-2081
Hossein Habibi, Graham Edwards, Liang Cheng, Haitao Zheng, Adam Marks, Vassilios Kappatos, Cem Selcuk, Tat-Hean Gan
Abstract Icing conditions in cold regions of the world may cause problems for wind turbine operations, since accreted ice can reduce the efficiency of power generation and create concerns regarding ice-shedding. This paper covers modelling studies and some experimental development for an ongoing ice protection system that provides both deicing and anti-icing actions for wind turbine blades. The modelling process contained two main sections. The first part involved simulation of vibrations with very short wavelength or ultrasonic guided waves (UGW) on the blade to determine optimal excitation frequency and transducer configuration. This excitation creates horizontal shear stress at the interface between ice and blade and focuses energy at the leading edge for de-bonding ice layers.
2015-06-15
Technical Paper
2015-01-2160
Alidad Amirfazli
Abstract The surfaces that shed drops helps with mitigation of icing. Shedding of drop depends on surface hydrophobicity, which becomes affected when exposed to water and/or UV. The hydrophobicity degradation of six (Spray SHS, Etched Al SHS, Hydrobead, Neverwet, Waterbeader, and WX2100) different super-hydrophobic surfaces (SHS), exposed to water or UV, were studied from the drop shedding perspective. Two methods were adopted for the hydrophobicity analysis. Among them, one is to study the contact angles (CA) and contact angle hysteresis (CAH) change at static state (i.e., no airflow) compared to the untreated surface. The other one is to analyze the change in critical air velocity (Uc) for a given drop exposed to airflow, on water/UV treated surfaces at room temperature (22 °C) and icing conditions (−1 and −7 °C).
2015-01-14
Journal Article
2015-26-0105
Prakash Kamat, Yogesh Aghav, Nitin Gokhale, M N Kumar
Abstract An innovative Diffusive Air Jet (DAJ) Combustion Chamber concept has been introduced in the present work. The DAJ Combustion Chamber design is based on the study of rate of heat release (ROHR) curve and its correlation with emission generation. The objective is to lower the trade-off between NOx and soot without sacrificing fuel economy of Direct Injection (DI) diesel engine. DAJ Combustion Chamber modifies ROHR curve to the desired one so that it lowers engine out emissions. To study its effect, a large bore, six cylinder engine with mechanical fuel injection system has been used. Three dimensional simulation software is used for the model calibration of basic reentrant cavity. Local emissions and ROHR curve have been studied using reentrant cavity shape. It has been modified to DAJ Combustion Chamber using Air Jet Chambers (AJCs). AJCs are positioned in the three dimensional model in such a way that they affect local in-cylinder emissions.
Viewing 1 to 30 of 4509