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Technical Paper

Engine Exhaust noise optimization using Sobol DoE sequence and NSGA-II Algorithms.

2019-06-05
2019-01-1483
Exhaust muffler is the most important component for overall vehicle noise signature. Optimized design of exhaust system plays a vital role in engine performance as well as auditory comfort. Exhaust orifice noise reduction is often contradicted by increased back pressure and packaging space. The process of arriving at exhaust design, which meets packaging space, back pressure and orifice noise requirements, is often manual and time consuming. Therefore, an automated numerical technique is needed for this multi-objective optimization. In current case study, a tractor exhaust system has been subjected to Design of Experiments (DoE) using SOBOL sequencing algorithm and optimized using NSGA-II algorithm. Target design space of the exhaust muffler is identified and modeled considering available packaging constrain. Various exhaust design parameters like; length of internal pipes, location of baffles and perforation etc. are defined as input variables.
Technical Paper

Improved measurement procedures for engine noise reduction with advanced microphones

2019-06-05
2019-01-1463
Introducing a new transducer concept has resulted in considerable reduction in setup time and at the same time improved accuracy and repeatability for engine bay noise transfer studies. The acoustic environment inside cars are one of the primary comfort parameters. This is made up of a number of contributions from drivetrain, auxiliary equipment, wind noise and tire noise, and all are influenced by the transfer from the source to the receiver. With the change from purely internal combustion engines to electrical or electrical assisted propulsion systems, a new set of noise sources are introduced in the engine compartment and this requires renewed focus on the transmission paths to the receivers inside the car cabin. Typically, one of the tools to study these mechanisms is by using a reverse transmission technique, placing a well-defined sound source in the receiver position inside the car and measure the resulting sound pressure levels in the engine compartment.
Technical Paper

Wind Noise Transmission Loss for Separated Flow Conditions

2019-06-05
2019-01-1469
The transmission of turbulent flow pressures through panels to the interior noise depends on the spatial matching of the pressure and vibration fields. Since the exterior pressure field on a moving vehicle includes both turbulent pressure and acoustic pressure, both need to be factored into a noise transmission loss calculation. However, these two exterior pressure fields have very different spatial patterns. This is further complicated when the exterior flow is separated from the surface due to an obstruction. This study uses wind tunnel and road tests to measure and model the wind noise transmission loss through the side glass of a vehicle. The results are seen to be very different from the traditional sound transmission loss curves for an acoustic pressure source.
Technical Paper

A Transient SEA Model for Transmission of Non-stationary Wind Noise

2019-06-05
2019-01-1473
Automakers have reported that passenger perception of vehicle interior wind noise is strongly correlated to the non-Gaussian and non-stationary character of the exterior aero-acoustic wind loading. It has been shown (Rouillard & Sek 2010) that leptokurtic non-Gaussian loading (Kurtosis κ>3) can be synthesized by non-stationary modulation of otherwise Gaussian random loading. This paper presents a transient statistical energy analysis (SEA) model for the aero-vibro acoustic transmission of non-stationary wind noise which uses the same approach - a modulation of otherwise Gaussian random fluctuating pressure loading, in each one third octave band. The authors have previously shown that the non-stationary character of random wind loading can be measured in a wind tunnel or on the road with a suitable surface pressure microphone array (Bremner et al SAE NVC 2017).
Technical Paper

Calculation process with Lattice Boltzmann and Finite Element methods to choose the best exterior design for wind noise

2019-06-05
2019-01-1471
Authors : Guillaume BAUDET, Cécile DUTRION, Rémi LORENZI, Félix GENDRE, Shanshan GENG Renault Automotive wind noise is a complex phenomenon. Noise in the cabin depends of: - The exterior loading due to the flow around the vehicle - The transfer loss of seals and panels - The acoustic transfer function of the cabin Each part of this cascading must optimized to have a good final performance. So the exterior design is a key parameter because it influence the loading (pressure field) on the vehicle panels and seals. For some years, we know that the exterior loading is split in two parts: - Hydrodynamic (or turbulent) loading with high wave number pressure field - Acoustic loading with low wave number pressure field In this paper, we present a calculation process which enables to predict the acoustic source created by the lateral window at high speed which has a major contribution to the interior noise.
Technical Paper

Turbulent Pressure Spectra for Separated Flow Conditions

2019-06-05
2019-01-1475
The magnitude of the turbulent pressure spectrum in fluid flow over an obstruction is usually much larger than in attached flow over a smooth surface. External features on a vehicle, such as windshield wipers, side mirrors and pillars which cause flow separation, are a major source of wind noise. The modeling of the pressure spectrum in separated flow is important for designing quiet vehicles. In this study wind tunnel tests have been performed with different shaped obstructions to measure and correlate the surface pressure spectra with flow parameters such as the pressure coefficient and separation size. The model by Chase for attached turbulent boundary layer pressures is generalized to apply to separated flow conditions.
Technical Paper

Mitigation of Community Noise from a Vacuum Excavator using Simulations

2019-06-05
2019-01-1480
Off-highway equipment operates in residential communities and must meet their radiated noise targets to be compliant with noise regulations and to be competitive in the marketplace. Traditional find and fix noise testing of late-stage prototype designs may cause launch delays, with intense time pressures that often result in missed opportunities to create excellent products with good value. Accurate simulation of noise from these machines allows noise targets to be assessed at each stage of product development, giving engineers time to develop low noise products without adding excessive manufacturing cost. Simulation of an early prototype of a new vacuum excavator showed excessive levels of radiated noise in two different frequency ranges. Further investigation of the simulation results of these two spectrum ranges indicated different noise mechanisms producing the excessive noise levels.
Technical Paper

Testing Methods and Signal Processing Strategies for Automatic Transmission Transient Multiplexed Pressure Data

2019-06-05
2019-01-1500
This paper covers the development of test cell hardware, testing procedures, and signal processing to capture and transform transient multiplex pressure data from multiple data acquisition for a highly instrumented 6 speed automatic transmission with a torque converter. A total of 37 pressure transducers were installed in the transmission, with 8 being on several clutches, valve bodies, and other various locations. The remaining 29 transducers were instrumented in the torque converter and transmitted signals via three telemetry transmitters. Each transmitter had the capability of handling 7 or 15 channels. The transmitters multiplexed through the channels in intervals of approximately 1 second. Due to the complexity of the instrumentation, a dyno controller, transmission controller, data acquisition system, and three telemetry receivers were used and synchronized.
Technical Paper

Vibro-acoustic transfer function measurement in vehicles using dodecahedral sound source and its application for material assessment

2019-06-05
2019-01-1532
NVH is an important aspect of vehicle design since it is one of the highest priorities and biggest influencing factors for customer while making decision to buy a vehicle. Hence, automotive engineers strive to design the superior cabin compartment to maintain pleasant levels of noise, vibration and the overall experience within the vehicle. To quantify the amount of energy transmitted between source and receiver region, transfer function analysis is primarily used. The focus of this paper is to measure vibro-acoustic transfer function using reciprocity approach instead of direct impact test measurement. It is found that the vibro-acoustic reciprocity holds true even for non-linear system like vehicle. The reciprocal measurement involves usage of dodecahedral sound source to acoustically excite the cabin from desired seating location and accelerometers are placed at all the locations of interest on vehicle body.
Technical Paper

A Comparison of Near-Field Acoustical Holography Methods Applied to Noise Source Identification

2019-06-05
2019-01-1533
Near-field Acoustical Holography (NAH) is an inverse process, in which sound pressure measurements made in the near-field of an unknow sound source can be used to reconstruct the sound field so that source locations to be clearly identified. NAH was originally based on performing spatial transforms of arrays of measured pressures and then processing the data in the wavenumber domain, a procedure that entailed the use of very large microphone arrays to avoid spatial truncation effects. Over the last twenty years, a number of different NAH methods have been proposed that can reduce or avoid spatial truncation issues: for example, Statistically Optimized Near-field Acoustical Holography (SONAH), various Equivalent Source Methods (ESM), etc.
Technical Paper

Optimal Pressure Relief Groove Geometry for Improved NVH Performance of Variable Displacement Oil Pumps

2019-06-05
2019-01-1548
Variable Displacement Oil Pump (VDOP) is becoming the design of choice for engine friction reduction and fuel economy improvement. Unfortunately, this pump creates excessive pressure ripples, at the outlet port during oil pump shaft rotation, causing oscillating forces within the lubrication system and leading to the generation of objectionable tonal noises and vibrations. In order to minimize the level of noise, different vanes spacing and porting geometries are used. This paper presents an optimization method to identify the best geometry of the oil pressure relief groove. The method integrates adaptive meshing, 3D CFD simulation, Matlab routine and Genetic Algorithm based optimization. The genetic algorithm is used to create the required design space in order to perform a multi-objective optimization using a large number of parameterized groove geometries. Results of this optimization method are discussed and a design guideline for the oil pressure relief groove is disclosed.
Technical Paper

Performance and emission studies in a heavy-duty diesel engine fueled with n-butanol and n-heptane blend

2019-04-02
2019-01-0575
N-butanol, as a biomass-based renewable fuel, has many superior fuel properties. It has a higher energy content and a higher cetane number than its alcohol competitors, methanol and ethanol. Previous studies have proved that n-butanol has the capability to achieve lower emissions without sacrifice on thermal efficiency when blended with diesel. (2017-01-0760) However, most studies on n-butanol are limited to low blending ratios, which restricts the improvement of emissions. In this paper, 80% by volume of n-butanol was blended with 20% by volume of n-heptane (namely BH80) and various engine parameters (EGR ratios, injection timings, intake pressures) on its combustion and emission characteristics are tested under different loads, 8, 12, 16 bar gross indicated mean effective pressure (IMEPg), respectively. The results showed that higher intake pressure promotes stable combustion of BH80 at 8 bar IMEPg.
Technical Paper

Effects of EGR, Swirl, and Cylinder Deactivation on Exhaust Temperatures of a Throttled Light-Duty Diesel Engine under Idle Conditions.

2019-04-02
2019-01-0544
Modern Diesel exhaust emissions control devices rely on catalysts for effective treatment. These catalysts must be maintained above a certain temperature, usually > ~200oC, to remain effective. Under low-load and idle conditions, the engine exhaust temperature of the engine may be significantly lower than the catalyst activation temperature. Particularly in congested urban settings, it can be common for light-duty vehicles to operate under idle and very low-load for considerable periods. This can lead to tailpipe emissions if the catalysts are not fully active. This study extends a previous study on the effects of throttling and post-injection on light-duty Diesel engine exhaust temperatures and emissions and includes the effects of EGR, in-cylinder swirl air motion, and cylinder deactivation. The baseline injection strategy was adapted from a 2014 Chevrolet Cruze having an engine similar to the light-duty GM engine used for this study.
Technical Paper

Added masses and volumes of stationary bodies in non-uniform streams

2019-04-02
2019-01-0661
The added mass is an abstract concept that found its usefulness in the determination of the forces and moments on bodies accelerating in an otherwise still fluid. It is based on the observation that a body accelerating relative to the surrounding fluid changes the kinetic energy of the fluid. In manner analogous to Newton’s second law of motion, the force that the body must exert to accelerate the surrounding fluid is identified as the product of the acceleration and the mass of the fluid, “added” to that of the body. Equivalent results can be obtained for a stationary body in unsteady flow, with the exception of fluid rotations. The connection between the added masses and the forces on stationary bodies in steady, non-uniform streams can be established using the long wave analogy. Similarly to the “volume times pressure gradient” formula in hydrostatics, of interest is rather the added volume than the mass of the fluid added to that of the body.
Technical Paper

Optical experiments on strong knocking combustion in rapid compression machines with different fuels

2019-04-02
2019-01-1142
Knocking combustion has become the greatest bottleneck of internal combustion engines with advanced combustion technologies for pursuing thermal efficiency limits. Because of the complexities of combustion conditions, the mechanism for strong knocking combustion in engines under different combustion modes is still not fully understood. In this study, synchronization measurement through simultaneous pressure acquisition and high-speed direct photography was performed, and strong knocking combustion for premixed iso-octane/air mixture was studied in a high-strength optical rapid compression machine with flat piston design. First, strong knocking phenomena under both spark-ignition and compression-ignition conditions are identified through varying initial thermodynamic conditions.
Technical Paper

Effect of Injection Pressure on Nozzle Internal Flow and Jet Breakup under Sub-Cooled and Flash Boiling Test Conditions

2019-04-02
2019-01-0286
Injection pressure plays a vital role in spray break-up and atomization. High spray injection pressure is usually adopted to optimize the spray atomization in gasoline direct injection fuel system. However, higher injection pressure also leads to engine emission problem related to wall wetting. To solve this problem, researchers are trying to use flash boiling method to control the spray atomization process under lower injection test conditions. However, the effect of injection pressure on the spray atomization under flash boiling test condition has not been adequately investigated yet. In this study, quantitative study of internal flow and near nozzle spray breakup were carried out based on a two-dimensional transparent nozzle via microscopic imaging and phase Doppler interferometery. N-hexane was chosen as test fluid with different injection pressure conditions. Fuel temperature varied from 112°C to 148°C, which covered a wide range of superheated conditions.
Technical Paper

Influence of Key Section Parameters of Exhaust Port on Flow Capacity

2019-04-02
2019-01-0200
A three-dimensional model of a diesel engine exhaust port was established. The reliability of modeling method and the exhaust port model were verified by the steady-flow test, PIV test and pressure field test. Based on the exhaust port model, the influence of the key section parameters such as inlet area S1, throat area S2, and outlet area S3 on the flow capacity of the exhaust port was studied. The results show that, under different pressure difference and exhaust back pressure conditions, the mass flow rate increases first and then converges with the increase of the area ratio of outlet and inlet or the area ratio of throat and inlet. With the increase of the relative pressure difference, the optimal area ratio of outlet and inlet decreases and converges to 1.02, but the optimal area ratio of throat and inlet increases and converges to 1.13.
Technical Paper

Characteristics of Impinging Spray and Corresponding Fuel Film under Different Injection and Ambient Pressure

2019-04-02
2019-01-0277
It has been found that the spray impingement on piston for SIDI engines significantly influences engine emission and combustion efficiency. Fuel film sticking on the wall will dramatically cause deterioration of engine friction performance, incomplete combustion, and substantial cycle-to-cycle variations. When increasing the injection pressure, these effects are more pronounce. Besides, the ambient pressure also plays an important role on the spray structure and influences the footprint of impinging spray on the plate. However, the dynamic behavior of impinging spray and corresponding film was not investigated thoroughly in previous literature. In this study, simultaneous measurements of macroscopic structure (side view) and its corresponding footprint (bottom view) of impinging spray was conducted using a single-hole, prototype injector in a constant volume chamber.
Technical Paper

A Simulation Study on Particle Deposition and Filtration Characteristics in Wall- Flow DPF with Inhomogeneous Wall Structure Using a Two-Dimensional Microcosmic Model

2019-04-02
2019-01-0995
A new two-dimensional wall-flow DPF microstructure model has been developed in this paper to investigate the particle deposition distribution in DPF channels and the deep-bed filtration process of DPF. The substrate wall of the DPF with a thickness of L is discretized into several slabs with a uniform thickness of Δy along the depth of the wall, and each slab has specific porosity. The filtration efficiency, pressure drop, particle deposition distribution and the dynamic deep-bed filtration process of the DPF with inhomogeneous wall structure are studied under various space velocities and permeabilities. Besides, the differences on DPF’s performance brought by the inhomogeneous wall structure are discussed by comparing with a homogeneous wall structure.
Technical Paper

Laminar burning velocities of high-performance fuels relevant to the Co-Optima initiative

2019-04-02
2019-01-0571
Co-Optimization of Fuels and Engines initiative of the U.S Department of Energy initiated investigations on several candidates of biofuels and blends for internal combustion engines. Several biofuels were selected by screening criteria, which were boiling point, toxicity, research octane number, octane sensitivity, laminar flame speed, and economical distribution system, etc. In this study, we focused our investigation on three of the fuels candidates; ethanol, 2-methylfuran, and methyl acetate. While there exist many studies for ethanol, there are only few studies on combustion characteristics of 2-methylfuran and methyl acetate in the literature. Measurements of properties such as ignition delay time and laminar burning velocity (LBV) are necessary for these fuels in order to understand their performance and applicability in engines. We present measurements of laminar burning velocities of these fuels at an initial pressure of 1 atm and initial temperature of 428 K.
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