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Particle size distribution and particle number emissions rather than legislated particulate mass emissions from diesel engines are subject of rising concern especially in the US and several Western European countries [1]*. Recently also particle number emissions from gasoline engines attracted much attention since these engines are supposed to emit very high numbers of ultrafine particles or even nano-sized particles [2]. The work described in this paper focused on the impact of modern diesel exhaust gas aftertreatment systems like diesel oxidation catalysts (DOC) and diesel particulate filter (DPF) on particle number emission. Especially the effect that these aftertreatment systems are supposed to significantly increase ultrafine particle numbers (because they may act like “reactors” actively producing ultrafine solid particles) gave reason for investigating the effects and mechanisms more in detail.

In the last few years the requirement to optimize powertrain noise and vibration has increased significantly. This was caused by the demand to fulfill the vehicle's exterior noise legislative limits in Europe, and by increased customer awareness for high ride comfort. Much effort concentrated on the engine and the powertrain as prime sources of noise and vibration in a vehicle. The cranktrain with its moving components is a significant source of noise and vibration excitation within the engine. This paper describes results of investigations to evaluate various design alternatives in respect to NVH. The influences of crankshaft material, of balancing rate and of secondary shaking forces are discussed, with the aim to evaluate these various design options.

Sound design of vehicle interior and exterior noise is becoming more and more important for the customer's impression of product quality. To accommodate for this, FEV has developed a sound design method that utilizes FEV VINS (Vehicle Interior Noise Simulation) to design series production relevant hardware modifications. Within a new internal research program, FEV's NVH specialists investigated the theory of musical harmonics and compared the results with engine acoustics in an effort to establish if and what mechanical acoustics can learn from musical harmonics. Looking at engine acoustics from the point of view of musical harmonic theory, the specific combination of half and integer engine orders in particular offers the possibility of creating harmonious noise content. Furthermore, we can estimate how the typical subjective evaluations derive from the integer and half engine orders that occur depending on the engine concept.

The electrification of vehicle propulsion has caused a significant change in many areas including the world of vehicle acoustics. Comments from the media currently range from “silently hums the future” to “electric car roars with V8 sound”. Decades of experience in designing brand-specific vehicle sound based on noise and vibration generated by combustion engines cannot be simply transferred to the upcoming vehicles driven purely by electric powertrains. Although electric vehicles are almost always considerably quieter than those powered by internal combustion engines, the interior noise is characterized by high-frequency noise components which can be subjectively perceived as annoying and unpleasant. Moreover, such disturbing noise is no longer masked by combustion engine noise. Fundamental questions regarding the sound design of electric vehicles have yet to be answered: it remains unclear what exactly the interior noise of an electric vehicle should sound like.

At the present time, combustion process effects on vehicle interior noise can be evaluated only when vehicle and engine are physically available. This Paper deals with a new method for the prediction of combustion process induced vehicle interior noise. The method can be applied already in early combustion system development and allows a time and cost efficient calibration optimization of engine and vehicle. After establishing appropriate transfer weighting functions (engine) and structure transfer functions (vehicle), audible vehicle interior noise is generated based on appropriate cylinder pressure analysis. Combustion process effects on interior noise can be judged subjectively as well as objectively. Thus, combustion process development at the thermodynamic test bench is effectively supported to achieve an optimal compromise with respect to fuel consumption, exhaust emission and interior noise quality.

This paper reflects an efficient and comprehensive approach for vehicle sound optimization integrated into the entire development process. It shows the benefits of early consideration of typical vehicle NVH features and of intensive interaction of P/T and vehicle responsibilities. The process presented here considers the typical restriction that acoustically representative prototypes of engines and vehicles are not available simultaneously at the early development phase. For process optimization at this stage, a method for vehicle interior noise estimation is developed, which bases on measurements from the P/T test bench only, while the vehicle transfer behavior for airborne and structure-borne noise is assumed to be similar to a favorable existing vehicle. This method enables to start with the pre- optimization of the pure P/T and its components by focusing on such approaches which are mainly relevant for the vehicle interior noise.

The current direction for Diesel combustion system development is towards homogenization, in order to reduce particulate and NOx emissions. However, a strong increase of carbon monoxide emissions (CO) is frequently noted in combination with enhanced homogenization. Therefore, the current investigation focuses on a detailed analysis of the particulate - CO trade-off using a laser-optical and multidimensional CFD investigation of the combustion process of a swirl HSDI system. The CFD methodology involves reduced kinetics for soot formation and oxidation and a three-step CO model. These models are validated by a detailed comparison to optical measurements of flow, spray penetration and the spatial distribution of soot, temperature and oxygen concentration. The results obtained show that high concentrations of CO occur as an intermediate combustion reaction product. Subsequently, CO and soot are oxidized in large areas of the combustion chamber.

The loads on the plain bearings of modern combustion engines increase continuously. Reasons for this development are increasing engine speeds on gasoline engines, growing cylinder peak pressures at diesel engines and both combined with the steady trend toward light weight concepts. The still significantly increasing power output of modern engines has to be combined with actions reducing the engine friction losses, as for example smaller bearing dimensions or lower engine oil viscosities. At the same time the comfort, lifetime and engine service interval targets are aggravating boundary conditions. This development leads to the point, where former approaches toward plain bearing layout reach their systematic limitations - a first indication are bearing failures, which occur even though all conventional layout criteria's are fulfilled. Further effects need to be considered to simulate the behavior of the plain bearing under the boundary conditions of a fired combustion engine.

Fuel consumption of a modern combustion engine is significantly influenced by the mechanical friction losses. Particularly in typical city driving, the reduction of the engine friction losses offers a remarkable potential in emission and fuel consumption reduction. The analysis of the engine friction distribution of modern engines shows that the piston group has a high share at total engine friction. This offers a high potential to optimize piston group friction. The paper presents results of recent research and development work in the field of the tribological system piston/piston ring/cylinder bore.

NVH refinement of passenger vehicles is crucial to customer acceptance of contemporary vehicles. This paper describes the vehicle NVH development process, with specific examples from a Diesel sedan application that was derived from gasoline engine-based vehicle architecture. Using an early prototype Diesel vehicle as a starting point, this paper examines the application of a Vehicle Interior Noise Simulation (VINS) technique in the development process. Accordingly, structureborne and airborne noise shares are analyzed in the time-domain under both steady-state and transient test conditions. The results are used to drive countermeasure development to address structureborne and airborne noise refinement. Examples are provided to highlight the refinement process for “Diesel knocking” under idle as well as transient test conditions. Specifically, the application of VINS to understanding the influence of high frequency dynamic stiffness of hydro-mounts on Diesel clatter noise is examined.

Within the PNGV program, very challenging targets in respect to vehicle fuel economy were set. These could not be met with today's gasoline engines and driveline concepts. One possible alternative approach is a hybrid vehicle with a small displacement engine that exceeds the fuel economy of conventional engines: the 1.2L DIATA (Direct-Injection-Aluminum-Throughbolt-Assembly) engine. Within the development of a CIDI engine the NVH aspects are of particular importance as the customer (i.e., driver) should not notice any negative difference to gasoline engines. Therefore, gasoline engine transparency in respect to NVH was one primary goal within the development process. This paper describes the implementation of NVH features into the engine design already in the initial concept design phases, and the consequent NVH optimization throughout the development phase.

The NVH optimization is a key issue for the development of future powertrains. This includes the radiated noise in terms of noise level and sound quality as well as the structure-borne noise excitation via the engine mounts. Experience shows that there are generally no single noise relevant components on modern powertrains which dominate the NVH behaviour. In contrast, a good NVH performance can only be achieved if the optimization process includes every single component and excitation. Only the combination of these optimized designs can lead to a first-class powertrain NVH. Within this paper the NVH optimization process of an existing 4-cylinder in-line spark-ignition powertrain is described. Examples for positive NVH designs are presented and their effect on the NVH behaviour are explained. Combining all positive NVH features into the engine resulted in a noise reduction of 3-5 dBA without any negative effect on fuel economy and performance.

Passenger cars with diesel engines have better fuel economy than cars with gasoline engines. Also diesel engines typically have lower HC and CO emissions than all but the very best, state-of-the-art gasoline engines. On the other hand, diesel NOx and particulate emissions are higher, but recent developments have significantly reduced diesel particulate emissions. While the regulated emissions from both engines are well known, there are relatively few data on the non-regulated emissions for modern diesel engines.

In the recent past, interior noise quality has developed into a decisive aspect for the evaluation of overall vehicle quality. At most operating points, the dominating interior noise share is generated by the powertrain. Interior noise simulation is a new tool for upgrading interior noise. Based on measurements of air- and structure-borne noise excitations caused by the powertrain, the interior noise shares are determined by applying the properties of the transfer paths. By superimposing the individual interior noise shares, the overall interior noise can be predicted. Well before the engine is operated in the vehicle for the first time, annoying interior noise shares, their causes and their transfer paths can be identified by subjective and objective analysis. This enables the engineer to focus on vital optimization measures as to excitations occurring at the engine as well as to transfer paths in the vehicle.

The reduction of particulate emissions from diesel engines is one of the most challenging problems associated with exhaust pollution control, second only to the control of NOx from any “lean burn” application. Particulate emissions can be controlled by adjustments to the combustion parameters of a diesel engine but these measures normally result in increased emissions of oxides of nitrogen. Diesel particulate filters (DPFs) hold out the prospect of substantially reducing regulated particulate emissions and the task of actually removing the particles from the exhaust gas has been solved by the development of effective filtration materials. The question of the reliable regeneration of these filters in situ, however, remains a difficult hurdle. Many of the solutions proposed to date suffer from high engineering complexity and/or high energy demand. In addition some have special disadvantages under certain operating conditions.

It is important to develop powertrain NVH characteristics with the goal of ultimately influencing/improving the in-vehicle NVH behavior since this is what matters to the end customer. One development tool called dB(VINS) based on a process called Vehicle Interior Noise Simulation (VINS) is used for determining interior vehicle noise based on powertrain level measurements (mount vibration and radiated noise) in combination with standardized vehicle transfer functions. Although this method is not intended to replace a complete transfer path analysis and does not take any vehicle specific sensitivity into account, it allows for powertrain-induced interior vehicle noise assessments without having an actual test vehicle available. Such a technique allows for vehicle centric powertrain NVH development right from an early vehicle development stage.

Combustion noise plays a considerable role in the acoustic tuning of gasoline and diesel engines. Even though noise levels of modern diesel engines reach extremely low values, they are still higher than those of conventional gasoline engines. On the other hand, new combustion procedures designed to improve fuel consumption lead to elevated combustion noise excitations as in case of today's direct injecting gasoline engines whose vibration excitation and airborne noise emissions are slightly increased during stratified operation. The partly conflicting development goals resulting from this can only be realized by integrating the NVH specialists' expertise into every development step from concept to SOP.

Blending gasoline with oxygenates like ethanol, MTBE or ETBE has a proven potential to increase the thermodynamic efficiency by enhancing knock resistance. The present research focuses on assessing the capability of a 2- and tert-butanol mixture as a possible alternative to state-of-the-art oxygenates. The butanol mixture was blended into a non-oxygenated reference gasoline with a research octane number (RON) of 97. The butanol blending ratios were 15% and 30% by mass. Both the thermodynamic potential and the impact on emissions were investigated. Tests are performed on a highly boosted single-cylinder gasoline engine with high load capability and a direct injecting fuel system using a solenoid-actuated multi-hole injector. The engine is equipped with both intake and exhaust cam phasers. The engine has been chosen for the fuel investigation, as it represents the SI technology with a strongly increasing market share.

NVH refinement is an important aspect of the powertrain development process. Powertrain NVH refinement is influenced by overall sound levels as well as sound quality. The sound quality and hence the level of powertrain NVH refinement can be negatively affected by the presence of excessive impulsive noise. This paper describes a process used to develop an understanding of impulsive powertrain noise. The paper begins with an introductory discussion of various sources of impulsive noise in an automotive powertrain. Following this, the paper outlines a process for identifying the source of the impulsive powertrain noise using examples from case studies. The remainder of the paper focuses on certain examples of impulsive noise such as Diesel knocking noise, injector ticking, impulsive cranktrain noise, and gear rattle. For these examples, the development of key objective metrics, optimization measures, and improvement potential are examined.

NVH refinement is an important aspect of the powertrain development and vehicle integration process. The depletion of fossil-based fuels and increase in price of gasoline have prompted most vehicle manufacturers to embrace propulsion technologies with varying degrees and types of hybridization. Many different hybrid vehicle systems are either on the market, or under development, even up to all-electric vehicles. Each hybrid vehicle configuration brings unique NVH challenges that result from a variety of sources. This paper begins with an introductory discussion of hybrid propulsion technologies and associated unique vehicle NVH challenges inherent in the operation of such hybrid vehicles. Following this, the paper outlines a two-dimensional landscape of typical customer vehicle maneuvers mapped against hybrid electric vehicle (HEV) operational modes.