Flub,th is the lubricant force acting on the thrust side of the piston flap in the normal direction. Flub,ring force of the lubricating oil film per unit length of the piston ring.
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Characteristics and challenges of automotive diesel engine design
- Classification of diesel engines
- Comparison between diesel engines and gasoline engines
- The history, characteristics, and challenges of diesel engines
Higher costs, mainly due to the sophisticated and expensive fuel injection equipment and the diesel particulate filter used in diesel engines. Lower engine rated speed, due to the limitation of slow combustion speed in the heterogeneous combustion in diesel engines.
The concept of systems engineering in diesel engine system design
- Principles of systems engineering
- Challenges of diesel engine system design in systems engineering
- Systems engineering in diesel engine system design – an attribute-driven design process
- Tools and methods of systems engineering
Strict design control of the interface between system elements is a critical topic in systems engineering. System modularization and integration of subsystems at interfaces is one of the main tasks in systems engineering. Systems engineering theory believes that system engineers use their technical knowledge of the entire system to guide system development (Fig. 1.4).
Different design concepts should be compared on the basis of total weighted performance rating, cost and the performance-cost ratio (or function-cost ratio, i.e. the value ratio).
The concepts of reliability and robust engineering in diesel engine system
- Key elements in reliability and robust engineering
- The concept of variability
- The concept of performance
- The concept of durability
- The concepts of quality, robustness, and quality loss function
- The concept of reliability
Internal environmental noise (also referred to as system interaction noise or proximity noise, i.e. the undesired effect of one subsystem on another, or subsystem interactions due to the variation of inputs from neighboring subsystems or of the operating environment of the vehicle system, e.g. variability in sensor signals, variance and drift of the airflow sensor, variability in the exhaust gas temperature or the composition of the engine's exhaust emissions). According to the definition given in the APQP (advanced product quality planning) manual jointly developed by Chrysler Corporation, Ford Motor Company and General Motors Corporation, durability is "the likelihood that an item will continue to perform at the expected level of customer, during the useful life without overhaul or rebuilding due to wear and tear'. The APQP manual also defined reliability as 'the likelihood that an item will continue to function at the customer's level of expectation at a measurement point, under specified environmental and duty cycle conditions'.
As summarized by Rausand and Hoyland (2004), until the 1960s reliability was defined as 'the likelihood that an item will perform a required function under certain conditions over a period of time'.
The concept of cost engineering in diesel engine system design
- Design for profit and design for value
- The need for engine system cost analysis
- The process of design target costing
- Objectives of engine system cost analysis
- Classification of cost and factors in cost analysis
- The method of engine system cost analysis
- Review of existing engine cost analysis methods
The cost design activity of a cost engineer in engine development is part of the overall financial analysis for the new product development. The cost engineer performs an engineering design function for the cost technology structure of the product. Instead, the engine system cost engineer focuses on the technical design of the cost structure of the engine, which is primarily related to materials/.
Cost-effectiveness is defined as the ratio of the dollar amount to the unit of effect.
Competitive benchmarking analysis
- The need for competitive benchmarking analysis
- Methods of competitive benchmarking analysis
- Basic engine system design parameters
- Competitive benchmarking analysis of engine performance
- Competitive benchmarking analysis in mechanical design
Engine weight per volume (also called weight density), which reflects the efficiency of the structural design and compactness of the engine. Engine specific gravity, which is the ratio of weight density to power density, i.e. the reciprocal of the power-to-weight ratio. Below is a brief discussion revealing the relationships between some of the above basic design parameters of an engine system.
The potential competitive benchmark parameters include the following: engine width; the geometric clearances between rotating moving parts and the inner wall of the engine block; engine length; and the 'CE/BE' ratio, which is the ratio of the cylinder-to-cylinder centerline distance to the cylinder bore diameter.
Subsystem interaction and analytical engine system design process
- Engine subsystem interaction
- Empirical engine design process
- Advanced analytical engine system design process
As a result, a precisely defined system design specification is not available at the beginning of the design process. The advanced analytical engine system design process is characterized by system engineering, simultaneous (or simultaneous) engineering, and advanced product quality planning (APQP). As the importance of diesel engine system design in product development emerges, the function of engine performance analysis takes a dominant role in the engine design process.
After the design specifications of the engine system have been determined, the design goals are further broken down to the level of the individual components.
Engine system design specifications .1 Overview of engine design specifications
- System performance specifications
- System durability
- System packaging
- System cost
Diesel engine system design specifications can be classified into four areas: performance, packaging, durability, and cost. The design specification for diesel engine system performance is expressed in terms of performance parameters and hardware (or calibration) parameters. The engine system design must verify the selected off-the-shelf solution prior to test verification.
Motor system Cost The specification plans the capital costs and operating costs for the motor technologies used.
Work processes and organization of diesel engine system design
- Characteristics and principles of diesel engine system design
- Theoretical foundation and tools for diesel engine system design
- Technical areas of engine performance and system integration
- Work processes of diesel engine system design
Designing diesel engine systems is a multidisciplinary applied field that has characteristics of the above academic disciplines. The full name of the performance branch of diesel engine systems design is Engine Performance and System Integration (EPSI). Two categories of research are identified for performance-related areas of diesel engine system design (Figure 1.34).
Overall process of engine development program Overall process of diesel engine system design Repeat and repeat the processes until successful validation.
New Modeling for Reliable Evaluation of the Effects of Parameter Variability on Vehicle Fuel Consumption, SAE Paper. He Y (2007), "Development of an Integrated Diesel Exhaust Aftertreatment Simulation Tool with Applications in Aftertreatment System Architecture Design", SAE Paper. Prince O, Morin G and Jouzeau C (2005), "Validation Test Optimization Based on a Statistical Approach for Diesel Engine Cylinder Head Reliability", SAE Paper.
Yan J, Rogalla R and Kramer T (1993), "Diesel Combustion and Transient Emissions Optimization Using Taguchi Methods", SAE paper 930600.
Engine durability issues
This chapter presents the theory and methods of durability and reliability analysis in diesel engine system design. Cavitation is a harmful phenomenon caused by the high-energy explosion of ruptured vapor bubbles originally created by unwanted dynamic pressures in a fluid system. Fouling and deposits can occur in situations such as injector coking, combustion chamber and valve seat soot deposits, and piston top deposits resulting in associated cylinder bore polishing.
Examples of durability faults include: the cracks in the piston, turbocharger, cylinder head, exhaust manifold, diesel particulate filter, rocker arm support plate and crankshaft; valve head and spring break; piston ablation and abrasion; bore polishing on the cylinder liner; VGT flag stuck; thermal deformation of the EGR valve; turbine blade-sheath interference due to high temperature creep; push rod nods; injector spool valve and spool failures;.
System design of engine performance, loading, and durability
- Engine system-level loading and durability design constraints
- Iterative design of system performance and durability
- The role of system durability engineers
Another example is the need to increase the design limit for the maximum allowable pressure in the exhaust manifold to achieve a high air-to-fuel ratio to reduce soot at rated power. Another example is selecting the size of the interstage cooler for a two-stage turbocharger to control the air temperature at the high-pressure stage compressor outlet. In order to consider structural robustness and reliability at an early stage of engine system design, analytical models must be developed to determine appropriate design durability limits.
In order to perform system optimization, the performance engineer needs design maps of durability as a function of loads or design constraints (Fig. 2.1).
The relationship between durability and reliability
At present, engine system design in the performance area has reached a highly accurate target design level under the assumption of predetermined stability design constraints. If the stability design constraints corresponding to satisfactory reliability are incorrectly defined, the correct design capability in the performance area cannot ensure a good design result in the stability/reliability area. At the early design stage it is unlikely that detailed finite element analysis or extensive experimental work will be carried out to seek appropriate maximum allowable design constraints.
Reliability can be assessed using customer service data and/or engine development data during the design/validation phase.
Engine durability testing
The worst cracking due to low cycle fatigue of the cylinder head may occur after a thermal cycle instead of full steady state load. It is important to investigate the correlation between engine dynamometer test cycles and real-world usage profiles in order to avoid over-design or under-design of the engine. To save testing time, accelerated durability tests are sometimes performed in the laboratory to accelerate wear and structural failure by deliberately increasing engine speed, load, or load cycle frequency.
At the end of the engine durability test, acceptance is determined based on experience and design margins are validated.
Accelerated durability and reliability testing
It is always important to correlate the following three sets of data to predict reliability: the predicted shelf life, the predicted reliability, and the collected reliability service data. A durability measure for B10 or B50 life can be derived by using a Weibull diagram, which shows the failure rate (usually on the vertical axis of the Weibull diagram) as a function of product life, number of running cycles, or vehicle distances traveled (on the horizontal axis of the Weibull diagram). The component failure characteristics (eg early failure, random failure) can be evaluated based on the beta slope of the Weibull curve.
Engine component structural design and analysis
System durability analysis in engine system design
For the preliminary structural calculation of the connecting rod, crankshaft, bearing and valvetrain, the structural loads can be calculated by using engine cycle simulation and multi-body dynamics of piston assembly, crankshaft or valvetrain to obtain the cylinder gas pressure load, the component inertial load and the vibration load. In the thermo-mechanical fatigue problems of the piston, cylinder head and exhaust manifold, the mechanical and thermal loads are calculated using engine cycle simulation. A simple FEA can be performed with the cycle simulation software (e.g. GT-POWER) to obtain the metal temperature distribution in the components.
Structural analysis usually begins with a deterministic model to analyze a particular pair of stress-strength relationship and factor of safety.
Fundamentals of thermo-mechanical failures .1 Overview of thermo-mechanical structural
- Fundamental concepts of mechanical failures
- Damage and damage models
- Thermo-mechanical failure modes
- Fatigue
Stress-strain curves are usually used to characterize the material structural behavior (eg the hysteresis loop, Fig. 2.2) in a loading cycle. The ultimate strength is the maximum stress that a material can withstand in compression, tension or shear before failure occurs (i.e. the peak on the engineering stress-strain curve in Fig. 2.2). The HCF life of the component is usually characterized by a stress-life curve (i.e. the s-Nf curve, Fig. 2.3b), where the magnitude of a cyclic stress is plotted against the logarithmic scale of the number cycles to failure.
Under a single type of cyclic loading (i.e., the plastic strain range remains constant in each cycle of loading), the plastic strain strain is usually predicted by the Manson-Coffi n relationship developed in the 1950s.
Diesel engine thermo-mechanical failures .1 Cylinder head durability
- Exhaust manifold durability
- Engine valve durability
- Cam fatigue and stress
The exhaust manifold consists of the intake flange, exhaust pipes (also called runners) and the exhaust flange with gaskets and bolts. Consequently, the temperature of the exhaust manifold gas is often used as a convenient indicator of the thermal load acting on the in-cylinder components. The gasket can withstand a much higher pressure than the normal operating pressure level of the exhaust manifold.
Predicting the thermal fatigue life of an exhaust manifold using simulation is important in both the concept design and detailed design stages.
