Deterioration Of Engine Research Articles

Aerodynamic performance test and flow visualization for reducing acoustic liner drag in grazing flow

We aim to reduce aerodynamic drag over an acoustic liner, which comprises of a perforated plate, a honeycomb core, and a rigid backplate, for aero-engine applications through both performance testing and flow visualization. Whereas the acoustic liner can attenuate engine noise, the structural characteristic of the liner surface causes the additional drag in grazing flow, resulting in deterioration of engine fuel efficiency. In this work, acoustic liner test pieces with various hole geometries are tested in the flow duct rig capable of generating sound wave and grazing air flow inside the duct. The static pressure drop measurement reveals that the perforation in the grazing flow direction wound increase the drag despite the same overall perforation for all test pieces. We further conduct the flow visualization using the test rig designed for water flow to be analogous to the air flow of the flow duct rig, and the analogy is based on Reynolds number defined with the friction velocity and the representative size of an acoustic liner. The result via particle image velocimetry represents the flow patterns causing the drag.

Studies on Performance Deterioration of a Low Bypass Turbofan Engine in Service

The performance deterioration of a low bypass turbofan engine is analyzed to find out its causes. The performance parameters are compared with their limitations for a specific throttle setting. Dirt buildup, soot deposit, de-twisting of turbine blades, malfunction of atomizers and fuel system accessories are found to degrade the engine health and performance before the intended service period. Periodic compressor wash and engine maintenance, cleaning or replacement of fuel filters and good assembly practices are found beneficial in addressing the issues and retaining the engine performance.

Research on a China 6b heavy-duty diesel vehicle real-world engine out NOx emission deterioration and ambient correction using big data approach.

China VI standard proposed higher requirements for durability of heavy-duty diesel vehicles emissions. Previous research which took advantages of both on-board sensors and big data approach to get the NOx deterioration factor was rather scarce. This paper used big data approach to study the deterioration of engine out NOx emission based on 254,622 km operation data getting from the on-board sensors or ECUs (Electronic Control Unit). Meanwhile, a formula for on-board NOx correction for ambient humidity and temperature had been fitted. The analyses revealed that the engine out NOx deterioration factor (DF) of the maximum weight steady-state condition was about 1.005 after 254,622 km durability test; as for transient conditions, the DF was not more than 1.092 during 254,622 km durability test. For a same steady working condition, the engine out NOx mass flow (g/h) was negatively linearly correlated with absolute humidity (Ha) (R2 = 0.997). If Ha was lower than 12 g/kg, Ha almost had no effect on engine out NOx concentration (ppm). Otherwise, there was also a negatively linear relationship between them (R2 = 0.978). It is hoped that the methods and conclusions of this paper could provide some enlightenment for future NOx emission deterioration research.

High-altitude performance and improvement methods of poppet valves 2-stroke aircraft diesel engine

Poppet valves 2-stroke (PV2S) diesel engine is promising to overcome the problems of low combustion performance and deteriorated emissions of conventional 2-stroke aircraft engines due to the lubricant leakage into cylinders. However, the high-altitude gas exchange and power performance of PV2S diesel engine with complex supercharging systems have been rarely studied, and the corresponding experimental methods are expected to be improved. To address these issues, a reformative experimental platform and one-dimensional simulation model are proposed to accurately predict the high-altitude performance and explore the improvement methods of a PV2S aircraft diesel engine with a combined supercharging system. Tracer gas method and pressure-based mass flow acquisition method are innovatively conducted in the platform to measure the gas exchange characteristics, which are validated with satisfactory accuracy and feasibility. The results indicate the performance deterioration of the PV2S engine is more severe than conventional 2-stroke engines due to the additional decrease of trapping efficiency. As the altitude increases from sea level to 8000 m, delivery ratio, trapping efficiency, charging efficiency and available brake power decrease by 22%, 27%, 43% and 61% respectively. Adjustments of valve overlap duration, as well as exhaust manifold length and chamber volume, can effectively improve the charging efficiency and brake power, which increase by 36.73% and 30.38% at 8000 m altitude, whereas at sea level they decrease 5.68% and 8.39% respectively. The study reveals the feasible application of PV2S diesel engine in aircraft propulsion and facilitates its use at high altitudes.

Influences of Waste Cooking Oil-Based Biodiesel Blends on PAH and PCDD/F Emissions from Diesel Engines in Durability Testing Cycle

In this study, the 60,000-km durability tests were performed on two diesel engines (EURO IV and EURO II) by using B10 (10% waste cooking oil + 90% diesel) and B8 (8% waste cooking oil + 92% diesel), respectively, to determine the impacts on the emissions of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCCD/Fs). The above emissions were measured per 20,000-km testing intervals. The highest total PAH mass concentrations were 38.2 and 25.6 μg Nm^(-3) before durability test by operating the EURO IV and II engines, respectively, and decreased 51-55% after 60,000-km operation. The dominant congeners of PAH emissions were naphthalene (＞ 45%), pyrene, and phenanthrene, which belonged to the LM-PAHs. The total PAH BaP_(eq) had different emission trends between the two engines during the durability tests. The highest level was 2.17 μg BaP_(eq) Nm^(-3) from EURO II engine before the test and reduced 84% after a 60,000-km cycle, when the total-BaP_(eq) emissions of EURO IV tended to increase from 0.0894 to 0.154 μg BaP_(eq) Nm^(-3) after the same test. The most dominant congener to the toxicity emissions was benzo(a)pyrene (~70%). Additionally, the PCDD/F emissions were tested in EURO IV engine by using B10. The PCDD/F concentrations of mass and toxicity approached the highest levels, 167 ng Nm^(-3) and 3.69 pg WHO-TEQ Nm^(-3), after 60,000-km and 20,000-km running cycles, respectively. The main dominant congeners were OCDD (＞ 50%) for mass, 2,3,7,8-TeCDD (＞ 35%) and 1,2,3,7,8- PeCDD (＞ 18%) for toxicity. Consequently, the use of WCO-biodiesel might reduce the PAH mass and toxicity emissions in older engine but had no significant effect in PAH and PCDD/F emissions during the deterioration of a newer engine.

Application Research of Electrical Supercharger for Improving Performances of Diesel Engine under Plateau Environment

Against the problems that the working performances deterioration of high-power engine under plateau environment, an electric supercharger system is designed by applying modern control and sensor technology, and after testing performances of the electric supercharger multiple times, the system is optimized according to the internal flow field distribution and export flow characteristics. The tests prove that the system which controlled by electric control device can achieve transient air supply rapidly. Then increased the air flow rate significantly, and it is able to recover the most of the power in low speed part, which propose the feasible way to the problem of engine intake air shortage under plateau environment.

Investigation of the combustion deterioration of an automotive diesel engine under transient operation

With increasingly stringent emission regulations and demand for fuel economy by the public, the combustion and emission problems of automotive diesel engines during transient operation have become vital and urgent issues. In this study, combustion deterioration has been experimentally analyzed using a heavy-duty turbocharged diesel engine running under transient conditions (constant speed and increasing torque). Optimization of the transient combustion process was performed by adjusting the fuel injection parameters. The results indicated that the notable combustion deterioration relative to steady state operation while transient was a function of the delay in the air-supply to the turbocharged engine, and took the form of combustion phasing delay, resulting in rapidly increasing smoke emission and fuel consumption. However, the delay in combustion phasing can be controlled by advancing the fuel injection timing, effectively increasing thermal efficiency. Unfortunately, smoke and NOx emissions increased at the same time. The deterioration in combustion phasing can also be improved by increasing injection pressure, resulting in decreased smoke emission while NOx emission increased. It is worth noting that the effective thermal efficiency first increased and then decreased as fuel injection pressure increased during transient operation. diesel engine, transient operation, combustion deterioration, injection parameters, combustion optimization

Impacts of low-pressure (LP) compressor’s deterioration of a turbofan engine upon fuel-usage of a military aircraft

AbstractSome in-service deterioration in any mechanical device, such as an aircraft’s gas-turbine engine, is inevitable. However, its extent and rate depend upon the qualities of design and manufacture, as well as on the maintenance/repair practices followed by the users. Deterioration of an engine normally results in the engine seeking a different steady operating-point relative to that for an engine without any deterioration. The variation in engine’s steady operating point leads to changes in the specific fuel consumption (SFC) and/or fuel flow (FF). Any rise in SFC and/or FF and thereby the increased quantity of fuel required is of prime importance in military aviation.For a military aircraft’s mission-profiles (consisting of several flight-segments), using a bespoke computer simulations, the consequences of low-pressure compressor’s deterioration of an aeroengine upon the weight of the fuel that has to be carried and consumed are predicted. This will help in making wiser management decisions (such as whether to remove an aero-engine from the aircraft for maintenance or to continue using it with some changes in aircraft’s mission profile). Hence improved engine utilization can be achieved, so resulting in lower overall life-cycle costs.

유전자 알고리즘을 이용한 항공기용 가스터빈 엔진의 단일 결함 진단에 대한 연구

유전자 알고리즘은 자연선택과 유전법칙을 적용하여 최적해를 탐색하는 방법으로, 본 연구에서 항공기용 가스터빈 엔진의 결함 진단을 위한 학습 알고리즘으로 사용되었다. 성능 저하를 고려한 구성요소는 압축기, 가스발생기 터빈, 동력 터빈이며, 설계점에서 엔진의 단일 구성요소에 대하여 각각 성능 저하 예측을 수행한 후, 이를 바탕으로 결함 진단을 수행하였다. 학습데이터 수의 증가가 유전자 알고리즘을 이용한 성능 저하 예측 및 결함 진단에 미치는 영향을 분석하였으며, 결과적으로 결함치에 대한 RMS 오차율이 모두 3% 이내로 예측됨을 확인하였다. Genetic Algorithms(GA) which searches optimum solution using natural selection and the law of heredity has been applied to learning algorithms in order to estimate performance deterioration of the aircraft gas turbine engine. The compressor, gas generator turbine and power turbine are considered for engine performance deterioration and estimation for performance deterioration of a single component at design point was conducted. As a result of that, defect diagnostics has been conducted. The input criteria for the genetic algorithm to guarantee the high stability and reliability was discussed as increasing learning data sets. As a result, the accuracy of defect estimation and diagnostics were verified with its RMS error within 3%.

Blade Erosion in Automotive Gas Turbine Engine

In this work, a study has been conducted to predict blade erosion and surface deterioration of the free power turbine of an automotive gas turbine engine. The blade material erosion model is based on three-dimensional particle trajectory simulations in the three-dimensional turbine flow field. The particle rebound characteristics after surface impacts were determined from experimental measurements of restitution ratios for blade material samples in a particulate flow tunnel. The trajectories provide the spatial distribution of the particle impact parameters over the blade surfaces. A semi-empirical erosion model, derived from erosion tests of material samples at different particulate flow conditions, is used in the prediction of blade surface erosion based on the trajectory impact data. The results are presented for the three-dimensional particle trajectories through the turbine blade passages, the particle impact locations, blade surface erosion pattern, and the associated erosion parameters. These parameters include impact velocity, impact angle, and impact frequency. The data can be used for life prediction and performance deterioration of the automotive engine under investigation.

Airworthiness of aircraft. Part 1. A stochastic model

It is argued that a stochastic approach to airworthiness analysis is necessary because of the inherent random variations in aircraft performance. It is then shown that the history of any performance variable in fleet service is best regarded as a ‘stochastic corrective process’, characterised by slow deterioration punctuated by rapid improvements at overhauls. Considering specifically the engine-out take-off climb performance of an aircraft, a model is proposed by taking into account gradient changes due to the deterioration of airframe, engine and propeller (if present), the frequency and effectiveness of overhauls, and the occurrence of deviations in the gradient achieved on any flight from the true capability of the aircraft. In analysing the effect of overhauls a distinction is made between maintenance by rectification and by replacement. In the model proposed a total of 14 parameters govern the probability distribution of the achieved gradient in fleet history, and consequently also the incident rate during take-off climb.