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It is a well-known fact that the exhaust emission characteristics of hydrogen fueled engines are extremely good. The external mixture formation - a hydrogen fuel supply method - has the merit of practically zero NOx emission level in the lean mixture range with the excess air ratio λ set at 2.0 or greater as well as the merits of simple mechanism and easy operation. However, the practical use of such engines has been impeded partly due to the occurrence of backfire where the excess air ratio λ is 2 to 3. In order to allow the practical use of the hydrogen fueled engines with external mixture formation, it is vital to determine the causes of backfire and to establish proper countermeasures. It is found through a recent study conducted on the mechanism of backfire that the abnormal electric discharge in the intake stroke is one of the causes of backfire.

The paper reports and evaluates the combustion pressures of electrolytically produced stoichiometric hydrogen-oxygen mixtures, spark-ignited inside a variable height (volume 0-250cc) ceramic piston cylinder arrangement. Ignition of mixtures was carried out at room temperature and absolute pressures varying between 5 and 180 kPa. Maximum combustion pressures were obtained from pressure-time traces and compared to a computer simulation model based on the first law of thermodynamics, ideal gas law and high temperature dissociation of combustion products. Ignition delay time and rate of pressure rise are also investigated. The results are to be used in a preliminary design of a combustion chamber of a hydrogen-oxygen fuelled engine. It was found that maximum combustion pressures are dependent on initial mixture pressure, initial water vapour content and surface area/volume ratio of combustion chamber.

The effect of humidity on the lean misfire limit and emissions from a lean burn, natural gas engine is described in this paper, along with a description of a practical humidity compensation method for incorporation into an electronic control system. Experiments to determine the effects of humidity on the lean limit and emissions are described. Humidity increases were shown to decrease the rate of combustion, reduce NOx emissions, and increase the levels of unburned hydrocarbon (HC) and carbon monoxide (CO) emissions. Data and calculations are also presented which demonstrate that increases in humidity will cause enleanment in a typical closed loop control system utilizing a universal exhaust gas oxygen (UEGO) sensor. A prototype system for humidity sensing and subsequent compensation based on these findings was implemented, and the system was found, through additional testing, to compensate for humidity very effectively.

One obstacle hindering the use of port fuel injection in natural gas engines is poor idle performance due to incomplete mixing of the cylinder charge prior to ignition. Fuel injection timing has a strong influence on the mixing process. The purpose of this work is to determine the impact of fuel injection timing on in-cylinder fuel distribution. Equivalence ratio maps have been acquired by Planar Laser Induced Fluorescence in an optical engine with a production cylinder head. Experimental results have been used to determine the injection timing which produces the most uniform fuel distribution for the given engine.

Knock-induced pressure waves in the combustion chambers of spark-ignited engines cause the engine block to vibrate at the same frequencies. These vibrations have different amplitudes at different locations on the engine block. This paper describes a project to find a location on the engine block where the amplitudes of the knock-induced vibrations are high enough to use in a knock control system. To find this location, six piezoelectric knock sensors were located on suitable regions of the engine block. Data were collected from the sensors at both knocking and non-knocking conditions using a high speed data acquisition system. After the data were transformed into the frequency domain, comparison of the knocking and non-knocking condition data indicated the frequencies and amplitudes of the knock-induced engine block vibrations. The location where knock-induced vibrations were transferred with the greatest amplitude was determined.

Natural gas presents several challenges to engine manufacturers for use as a heavy-duty, lean burn engine fuel. This is because natural gas can vary in composition and the variation is large enough to produce significant changes in the stoichiometry of the fuel and its octane number. Similarly, operation at high altitude can present challenges. The most significant effect of altitude is lower barometric pressure, typically 630 mm Hg at 1600 m compared to a sea level value of 760 mm. This can lower turbocharger boost at low speeds leading to mixtures richer than desired. The purpose of this test program was to determine the effect of natural gas composition and altitude on regulated emissions and performance of a Cummins B5.9G engine. The engine is a lean-burn, closed loop control, spark ignited, dedicated natural gas engine. For fuel composition testing the engine was operating at approximately 1600 m (5,280 ft) above sea level.

A Key Life Test is an accelerated test designed to detect a major component failure mode. The Key Life Test process will be outlined, as applied to predicting the life and reliability of an automotive synchronous timing belt. The main objective of this type of testing is the development of a model to improve quality by designing reliability into the product. A math model will be described to assess severe customer usage, determine the test conditions and acceleration factor and is used to find the timing belt life and reliability. The application of Probabilistic Methods will be explained to predict the belt life and reliability, after the model has been correlated against the test results obtained. It will be shown that the design can be optimized to improve the timing belt reliability using the model.

The paper discusses some statistical aspects of warranty repair predictions in automotive industry. The existing Renewal Process approach to model a single component repairable system is reviewed, and its limitations in terms of applicable TTF distributions are discussed. The Superimposed Renewal Process approach to model a multi component repairable system is then considered and its limitations in terms of the error of the superimposed aggregation are pointed out. Finally, a Monte Carlo approach is presented and its advantages over the conventional methods are discussed.

Performing life tests on products in order to guarantee quality is a necessity. No systematic procedure is available for developing life tests for components, subsystems, and systems in order to minimize the cost. Life tests are developed uniquely from one among components, subsystems, and systems without incorporating a systems approach toward developing the tests. To guarantee that proper tests have been planned in a cost effective way for components, subsystems, and systems a methodology is required. This paper has proposed a cost effective strategy of developing life tests for systems.

This paper provides an overview of the approach taken by the Federal Aviation Administration for tracking and evaluating the performance of the engines installed on Flight Inspection Aircraft. The Flight Insepction Aircraft are used to verify the accuracy of domestic and international navigational equipment. The engine recorded data enables maintaining operational efficiency and permits timely maintenance actions.

Providing an automated data collection system together with a regulatory flight recorder function, the Engine Performance Trend Monitor / Structural Integrity (EPTM/SI) System reduces flight crew workload and improves accuracy of collected data by using a lightweight, compact, survivable recording system. This combination system automatically monitors flight loads and aircraft usage for transfer to an Aircraft Structural Integrity (ASIP) program, and records engine trend data for input to engine trend monitoring software while maintaining a record of the last eight hours of flight data. The purpose of this paper is to describe the system components, capabilities, and growth options.

Separated flows and subsequent formation of shear layers are important fluid processes which play a dominant role in numerous engineering applications. Prediction of this fluid process is an important element in the design and analysis of highspeed vehicles and, ultimately, in the performance and trajectory analysis. The prediction methodology used in the current study includes the numerical solution of the Navier-Stokes equations on a multi-block grid system. Several turbulence models are used to investigate their performance for compressible, turbulent, separated and shear layer flows. The computational results are compared to available experimental data.

LEWI3DGR has proven itself a useful all-around tool for icing tasks at Gulfstream. The code's ability to handle lifting as well as non-lifting surface icing calculations with equal ease have made it the company icing workhorse. Implementation is straightforward, and results are reliable. LEWI3DGR analyses detailed herein have provided the basis for sucessful flight test and certification efforts.

The removal of tetraethyl lead (TEL) from U.S. automotive gasoline has caused concern within the general aviation (GA) community because of possible legislated environmental or supply restrictions on TEL, an essential ingredient in existing high octane aviation gasolines (avgas). At the same time, the GA industry which was besieged by numerous product liability suits in the past has seen a resurgence since the passage of the GA Revitalization Act in 1994. Because aircraft typically remain in service for many years, the survival of the industry may well depend on the availability of a high octane unleaded gasoline that provides a safe level of power and antiknock performance to the existing fleet. This paper describes the tools and techniques used by one team to develop fuels that provide the required antiknock quality while meeting most of the other criteria of the existing specification for high octane avgas: ASTM D 910, Standard Specification for Aviation Gasolines.

New concepts for the delivery of products from avionics suppliers to aircraft manufacturers are becoming available to meet contemporary standards of product quality, delivery performance and inventory management. These concepts promise to transform the traditional relationship between avionics supplier and aircraft manufacturers. Since these concepts are most applicable to high-volume production, certain piston-engine light aircraft programs are particularly suitable applications for these new concepts.

This paper elaborates on current testing techniques used to determine an aircraft's attenuation characteristics in the presence of High Intensity Radiated Fields (HIRF). This is not a theoretical discussion for the Electromagnetic expert, but rather a practitioner's overview for the avionics/electrical engineer who must oversee HIRF testing. Three testing techniques used to determine the attenuation of an aircraft will be discussed: (1) the Low Level Direct Drive (LLDD) test used for the 10 kHz to the first aircraft resonance frequency; (2) the Low Level Swept Current (LLSC) test used for the 1 to 400 MHz frequency band; and (3) the Low Level Swept Fields (LLSF) test used for the 100 MHz to 18 GHz frequency band.

Technological advances provide the means to implement designs to give the pilots improved and safer control of an aircraft throughout the whole flight regime from gate to gate. These advances also give the passengers access to everything they need to have a flying office and for en route entertainment all at feasible costs. These same advances in technology present many complex design, certification and operational issues that must be addressed to effectively use the information that is available for aircraft systems, flight crew and passenger use. This paper describes some of the issues involved and some of the avionics advances that can be expected.

An analytical/computational method of computing radiated noise from ducted rotor due to inflow distortion and turbulence is presented. Analytical investigations include an appropriate description of sources, the cut-off conditions imposed on the modal propagation of the pressure waves in the annular duct, and reflections at the upstream end of the duct. Far field sound pressure levels at blade passing frequency due to acoustic radiation from a small scale low speed fan are computed. Theoretical productions are in reasonable agreement with experimental measurements.

Control of structure borne noise transmission into an aircraft cabin generated from component excitation, such as rotor/engine vibration imbalance or firing excitations or from auxiliary equipment induced vibrations, can be studied empirically via impedance characterization of the system components and application of appropriate component coupling procedures. The present study was aimed at demonstrating the usefulness of such impedance modeling techniques as applied to a Bell 206B rotorcraft and a Cessna TR182 general aviation aircraft. Simulated rotor/engine excitations were applied to the assembled aircraft systems to provide baseline structure borne noise transmission data. Thereafter, impedance tests of the system components were carried out to provide a data base from which system component coupling studies were carried out.

The Federal Aviation Administration (FAA)'s analysis of commuter aircraft accidents and ongoing research has indicated that the crashworthiness capabilities of smaller aircraft may be questionable. The small size of these aircraft results in a stiff structure and consequently higher impact loads experienced by the occupants. In 1993, the FAA issued a Notice of Proposed Rule Making (NPRM) 93-71 to increase the deceleration pulse amplitude of the sled tests under the Test-1 conditions (60-degree test) to 32G for the commuter type aircraft. To meet this condition, the seat design must exploit the energy absorption potential for its structural components. Energy absorbing components may include the seat legs, seat pan, and seat cushion. The intent is to design the seat so that it strikes well beyond the elastic limit to absorb the energy of the impact. To date, no seat has yet been able to pass the proposed criteria with an acceptable limit on the lumbar load (1500 pounds).