Multiphase CFD-CHT Analysis and Optimization of the Cooling Jacket in a V6 Diesel Engine

<div class="section abstract"><div class="htmlview paragraph">The paper presents a combined experimental and numerical activity carried out to improve the accuracy of conjugate heat transfer CFD simulations of a high-performance S.I. motorbike engine water cooling jacket. The computational domain covers both the coolant jacket and the surrounding metal components (head, block, gasket, valves, valve seats, valve guides, cylinder liner, spark plug).</div><div class="htmlview paragraph">In view of the complexity of the modeled geometry, particular care is required in order to find a tradeoff between the accuracy and the cost-effectiveness of the numerical procedure. The CFD-CHT simulation of water cooling jackets involves many complex physical phenomena: in order to setup a robust numerical procedure, the contribution of some relevant CFD parameters and sub-models was discussed by the authors in previous publications and is referred to [<span class="xref">1</span>, <span class="xref">2</span>, <span class="xref">3</span>, <span class="xref">4</span>].</div><div class="htmlview paragraph">Among the formers, the effects of a proper set of boundary conditions and a detailed representation of the physical properties of the involved materials were evaluated. Among the latter, the contribution of a two-phase approach taking into account the effects of phase transition within the engine coolant was considered.</div><div class="htmlview paragraph">The CFD-CHT setup is now applied to investigate and understand the origin of a critical engine behavior occurring at the engine test bench under a severe reliability test. Additional sub-models are introduced and their impact on the results is discussed. Different engine operations are modeled and a detailed analysis of the many thermo-mechanical factors influencing the engine fatigue strength is carried out.</div><div class="htmlview paragraph">At the end of the process, CFD simulations are able to correctly capture and understand the origin of the engine failure, thus leading to a faster and more effective design modification.</div></div>

<div class="htmlview paragraph">The effects of the swirl level on the fresh air charge distribution is studied by using a multidimensional computer code for a uniflow type two-cycle diesel engine geometry. The flow is assumed to be axisymmetric. The inlet ports are simulated as an annular opening around the liner, and the exhaust valves are simulated as an annular slot in the cylinder head. Calculations are performed from exhaust valve opening to TDC for a large range of inlet port angles (10-30°). Results are presented in terms of velocity vector plots together with swirl velocity, and fresh charge contour plots.</div> <div class="htmlview paragraph">During the valves open period, the calculations indicate the presence of two vortices in the radial-axial flow plane as previously observed by Diwakar. The first one is near the liner wall (named as wall vortex) and the other is near the symmetry axis (named as the backflow vortex). The incoming fresh air tends to flow toward the cylinder head between these two vortices with reverse flows on the liner wall and near the symmetry axis. Increasing the swirl increases the strength and the region covered by the backflow vortex, redirects the upward fresh charge to a larger radius, and restricts the short-circuiting of the fresh air to the exhaust valves. This increases the trapping of fresh charge and the scavenging efficiency.</div> <div class="htmlview paragraph">Calculations from the exhaust valve closing to TDC show that: <ol class="list nostyle"> <li class="list-item"><span class="li-label">1)</span> <div class="htmlview paragraph">The size of the backflow vortex is reduced as the port is closed and diminishes immediately thereafter. The wall vortex is present up to 60° CA BTDC when the squish effects generated by the piston motion becomes dominant.</div></li> <li class="list-item"><span class="li-label">2)</span> <div class="htmlview paragraph">Fresh charge is not completely mixed with the residual gases even at TDC. There is about 11-17% difference in the fresh charge concentrations at the highest and lowest fresh charge locations at TDC. The inlet port angle (engine swirl level) seems to increase the magnitude of this stratification slightly, but more importantly, it changes the location of this charge stratification considerably. At low swirl levels (port angle 10°), the low fresh charge region is located near the mid-radius of the bowl, and the maximum fresh charge is in the clearance volume between the piston and the bowl. At high swirl levels (port angle 30°), the maximum fresh charge is compressed toward the bowl belly, and the low concentration region is both in the clearance volume and on the cylinder head near the axis. At medium swirl levels (port angle 20), the fresh charge covers the midsection of the bowl, while the residual gases are restricted only within the clearance between piston and engine head.</div></li> </ol></div> <div class="htmlview paragraph">For the diesel engine application and to enhance the mixing of the fuel spray with the fresh air, the residual gas-fresh air stratification pattern of the medium swirl case is better than both the high swirl and low swirl cases.</div> <div class="htmlview paragraph">In addition to the wall vortex (generated by flow separation above the port) and the Backflow Vortex (generated by the swirl velocity field), a new vortex pattern named as the Head Vortex is identified. The mechanism for the Head Vortex development is recognized as the stagnation of the fresh air jet on the cylinder wall rather than on the engine head. The presence of the head vortex changes the mixing rate between the residual gases and the fresh air considerably. The development of the concentration profiles to these final shapes is demonstrated. The effects of the engine swirl level on the mixing of the fresh charge with the residual gases are investigated in terms of the mixing rates and the maximum concentration difference within the flow field.</div>

<div class="section abstract"><div class="htmlview paragraph">Today engine downsizing, weight reduction, boosting, etc. are widely used in modern combustion engine designs in order to increase power output, improve fuel economy, and reduce emission. However utilizing of these advanced technologies is making the engine less rigidity and resulting in potential fretting damages on any contact surfaces of engine components due to higher cyclic relative motions. The leakage failure of the cylinder-head sealing system induced by fretting damage on engine head and block deck surfaces is the one of major failure modes in the modern combustion engine. In this paper, the characteristics and failure modes of the MLS head gasket sealing system is introduced first. The fretting mechanism between MLS head gasket and engine head and block is then investigated and a fretting damage parameter and a damage criterion as well are defined and established to evaluate the crack nucleation or wear initiation. Also it is important to identify two types of loads during engine operation in the fretting damage calculation. The developed methodology is successfully verified through a good correlation between CAE analysis and actual engine thermal shock tests. This approach and results discussed in this paper provides a good guidance for the fretting damage analysis, assessment, and predicting of engine head and block deck surfaces.</div></div>

<div class="htmlview paragraph">Forty-one short-trip service tests were run using 1964-1969 model U.S. passenger cars and 19 commercial or experimental oils evaluating several aspects of engine rusting. These factors included differences in rusting severity among engine models, effects of fuel variables on rusting, and the effects of oil additive type and concentration on rusting.</div> <div class="htmlview paragraph">Rusting severity varied widely among engine models, but different engines ranked similarly the rust protection provided by oils with differing additive treatments.</div> <div class="htmlview paragraph">Use of either nonleaded gasoline or LPG instead of leaded gasoline greatly reduced engine rusting.</div> <div class="htmlview paragraph">At equivalent additive treatment levels, several magnesium sulfonates provided better rust protection than did certain calcium sulfonates, calcium phenates, or a barium sulfonate. Rust protection increased greatly and approximately linearly with increasing magnesium content.</div> <div class="htmlview paragraph">From these tests, and those reported by others, there appear to be three requirements for engine rusting to occur:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">1.</span> <div class="htmlview paragraph">Addition to the crankcase of corrosive products from the gasoline lead antiknock scavengers and combustion products.</div> </li> <li class="list-item"> <span class="li-label">2.</span> <div class="htmlview paragraph">Cold engine operation, permitting condensation and accumulation of corrosive products in the oil.</div> </li> <li class="list-item"> <span class="li-label">3.</span> <div class="htmlview paragraph">Depletion of rust-preventing oil additives.</div> </li> </ol> </div> <div class="htmlview paragraph">Since the first two requirements are at present largely uncontrolled from the customers' standpoint (most gasolines are leaded and contain scavengers, and winter weather is cold in many areas), the only other apparent avenue for improving the rust protection provided to current-design engines using leaded gasolines is better rust-preventing additives in the oil.</div>

<div class="htmlview paragraph">The effects of engine operating conditions on the octane requirement and the resulting knock-limited output were studied on a single cylinder engine using production cylinder heads. A 4-valve cylinder head with port deactivation was used to study the effect of fuel octane, inlet air temperature, coolant temperature, air/fuel ratio, compression ratio and exhaust back pressure. The effect of the thermal environment was studied in more detail using separate cooling systems for the cylinder head and engine block on a 2-valve cylinder head.</div> <div class="htmlview paragraph">The results of this study compared closely with results found in the literature even though the engine and/or operating conditions were quite different in many cases. Guidelines on the effect of various parameters on the octane requirement of an engine can be summarized as follows:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"><div class="htmlview paragraph">Spark Advance: 1 ON/1° SA</div></li> <li class="list-item"><div class="htmlview paragraph">Intake Air Temperature: 1 ON/7 K</div></li> <li class="list-item"><div class="htmlview paragraph">Air/Fuel Ratio: peaks at 5% rich of stoichiometric, decreases by around 2 ON / air/fule ratio around peak</div></li> <li class="list-item"><div class="htmlview paragraph">Intake Pressure: 3-4 ON/10 kPa</div></li> <li class="list-item"><div class="htmlview paragraph">Compression Ratio: 5 ON/CR</div></li> <li class="list-item"><div class="htmlview paragraph">Exhaust Back Pressure: 1 ON/30 kPa</div></li> <li class="list-item"><div class="htmlview paragraph">Coolant Temperature: 1 ON/10 K (Similar effect of head and block temperature., Larger effect at low speed.)</div></li> </ul> </div>

<div class="htmlview paragraph">The use of graphical dynamic system simulation software is becoming more popular as automotive engineers strive to reduce the time to develop new control systems. The use of model-based control methods designed to meet future emission and diagnostic regulations has also increased the need for validated engine models. A previously validated, nonlinear, mean-torque predictive engine model<span class="xref">*</span> is converted to MATLAB / SIMULINK<span class="xref"><sup>†</sup></span> to illustrate the benefits of a graphical simulation environment. The model simulates a port-fuel-injected, spark-ignition engine and includes air, fuel and EGR dynamics in the intake manifold as well as the process delays inherent in a four-stroke cycle engine. The engine model can he used in five ways:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"><div class="htmlview paragraph">As a nonreal-time engine model for testing engine control algorithms</div> </li> <li class="list-item"><div class="htmlview paragraph">As a real-time engine model for hardware-in-the-loop testing</div> </li> <li class="list-item"><div class="htmlview paragraph">As an embedded model within a control algorithm or observer</div> </li> <li class="list-item"><div class="htmlview paragraph">As a system model for evaluating engine sensor and actuator models</div> </li> <li class="list-item"><div class="htmlview paragraph">As a subsystem in a powertrain or vehicle dynamics model</div> </li> </ul> </div> <div class="htmlview paragraph">Although developed and validated for a specific engine, the model is generic enough to be used for a wide range of spark-ignition engines. Modular programming techniques reduce model complexity by dividing the engine and control system into hierarchical subsystems.</div>

<div class="section abstract"><div class="htmlview paragraph">The reduction of CO<sub>2</sub> emissions is one of the most important challenges for the automotive industry to contribute to address global warming. Reducing friction of internal combustion engines (ICEs) is one effective countermeasure to realize this objective. The improvement of engine oil can contribute to reduce fuel consumption by reducing friction between engine parts.</div><div class="htmlview paragraph">Electrification of ICE powertrains increases the overall efficiency of powertrains and reduces the average engine oil temperature during vehicle operation, due to intermittent engine operation. An effective way of reducing engine friction is to lower the viscosity of the engine oil in the low to medium temperature range. This can be accomplished while maintaining viscosity at high temperatures by reducing the base oil viscosity and increasing the viscosity modifier (VM) content to raise the viscosity index (so-called “flat viscosity” concept). However, reducing the base oil viscosity increases volatility loss and may cause an increase in oil consumption as a trade-off effect.</div><div class="htmlview paragraph">ASTM D5800 (NOACK test) has been utilized as an industry standard test since the 1930s to measure the evaporative loss of engine oils related to evaporative oil consumption. However, some reports indicate that standard NOACK does not correlate well with actual engine oil consumption. A new evaporative index with better correlation is necessary for further engine oil technology development.</div><div class="htmlview paragraph">This study investigated which physical properties of engine oil can express the evaporation rate related to evaporative engine oil consumption in actual engines. As a result, a modified NOACK test at 150°C, which is in the temperature range of the cylinder bore, showed good correlation with evaporative oil consumption in actual engine operation. This modified NOACK test has potential as a new evaporative index to realize new concept oils with flat viscosity properties.</div></div>

<div class="htmlview paragraph">Evaluations were made of the short-term (5 minute) durability at high temperatures of 85 mm outer diameter ceramic radial turbine rotors made of silicon nitride using an improved hot gas spin test rig.</div> <div class="htmlview paragraph">Under no load conditions, the rotors withstood a maximum turbine tip speed (Ut) of 550 m/s without bursting at a turbine inlet gas temperature (TIT) of 1240°C.</div> <div class="htmlview paragraph">Under partially loaded conditions, they withstood up to Ut of 500 m/s at TIT of 1280°C without bursting.</div> <div class="htmlview paragraph">The test results indicated that the knee point temperature in terms of TIT at which the failure tip speed decreased sharply was about 40°C higher under partially loaded condition than under no load condition.</div> <div class="htmlview paragraph">The temperature and stress distribution in the turbine in the hot gas spin test were calculated by the finite element analysis, which supported the dependence of the knee point temperature in terms of TIT at spin test on load condition.</div>

<div class="section abstract"><div class="htmlview paragraph">State-of-the-art motorcycle engines consist of numerous variable components and require a powerful motor management to meet the growing customer expectations and the legislative requirements (e.g. exhaust and noise emissions, fuel consumption) at the same time. These demands are often competing and raise the level of complexity in calibration. In the racing domain, the optimization requirements are usually higher and test efficiency is crucial. Whilst the number of variables to control is growing, the time to perform an engine optimization remains the same or is even shortened. Therefore, simulation is becoming an essential part of the engine calibration optimization. Considering the special circumstances in racing, involving valuable hardware, as well as extremely short development and calibration iteration loops, only transient testing is possible.</div><div class="htmlview paragraph">By utilizing model-based testing and optimization, Ducati Corse, the racing team division of the well-known motorcycle manufacturer Ducati, improved the ability to optimize their race engines efficiently. By using an engine model it is possible to make extremely quick calibration adaptations. All parameters can easily be optimized with respect to potential constraints without running the engine on a testbed. Moreover, the re-use of the engine model for co-simulations is applicable and sharing it with other departments in the company is possible to increase efficiency even more.</div><div class="htmlview paragraph">AVL CAMEO™ - the intelligent automated calibration environment - supports all engine optimization requirements with a consistent workflow from the task definition to the verification. For this specific racing use case, the software solution was implemented for the test planning using DoE (Design of Experiment), the data plausibility check and the empirical engine modeling. In addition, AVL CAMEO™ was the tool for realizing the model-based optimization and map creation.</div><div class="htmlview paragraph">With the implementation of the model-based approach, the motorcycle manufacturer has successfully improved the engine performance optimization. An exact model of the engine is now available which supports a deep understanding of the engine behavior. Through realizing this calibration approach, quick office and race track adaptations are possible and alternative optimizations for different tracks or conditions are easy to execute.</div></div>

<div class="section abstract"><div class="htmlview paragraph">An Automotive vehicle is subjected to run in various ambient conditions at different load conditions. For an SUV with off-roading capability, it becomes more important to size the cooling module for optimal performance.</div><div class="htmlview paragraph">The heat exchangers like AC condenser and radiator dimensions majorly defines the heat rejection capacity suitable for the respective powertrain configuration of a vehicle. Subsequently, the air flown over the heat exchangers will be dependent on the radiator fan capacity along with the vehicle speed.</div><div class="htmlview paragraph">However, being an SUV with off-roading capability, the need arises to simulate the combination of various speed ranges, in addition to the different loading conditions involved. Considering the various conditions, the ram air required for efficient cooling should be adequate for the heat exchangers to attain optimal performance. Hence, radiator & fan motor sizing plays an important role in the Powertrain as well as Cabin cooling performance.</div><div class="htmlview paragraph">The present study was conducted to check the adequacy of the radiator & fan motor sizing, and their effects to improve the powertrain and cabin cooling performance of the vehicle.</div><div class="htmlview paragraph">Also, this paper covers the experiments conducted and their respective findings on optimization of cooling performance and methodology for same.</div></div>

<div class="section abstract"><div class="htmlview paragraph">This paper reports 1D and 3D CFD analyses aiming to improve the gas-dynamic noise emission of a downsized turbocharged VVA engine through the re-design of the intake air-box device, consisting in the introduction of external or internal resonators.</div><div class="htmlview paragraph">Nowadays, modern spark-ignition (SI) engines show more and more complex architectures that, while improving the brake specific fuel consumption (BSFC), may be responsible for the increased noise radiation at the engine intake mouth. In particular VVA systems allow for the actuation of advanced valve strategies that provide a reduction in the BSFC at part load operations thanks to the intake line de-throttling. In these conditions, due to a less effective attenuation of the pressure waves that travel along the intake system, VVA engines produce higher gas-dynamic noise levels. The worsening of the engine gas-dynamic performance can be compensated with a partial re-design of the air-box device, without significantly penalizing the engine power output. In order to find new design configurations of the air-box device capable of improving the noise levels, different numerical models can be successfully employed.</div><div class="htmlview paragraph">In the present work, a detailed 1D engine model is firstly developed and validated against the experimental data at full load operations. 1D model is realized within GT-Power™ software and it utilizes proper user routines for the modeling of the turbulence and combustion process and for the handling of different intake valve strategies. The 1D engine model also includes a refined user model of the turbocharger able to better describe the acoustic behavior of the device.</div><div class="htmlview paragraph">The engine model allows for the prediction of the main overall engine performances and the gas-dynamic noise with good accuracy. It also provides a first estimation of the gas-dynamic noise and gives reliable boundary conditions for the subsequent unsteady 3D CFD analyses, allowing to obtain a more accurate noise prediction.</div><div class="htmlview paragraph">A proper Helmholtz resonator is designed and virtually installed along the inlet pipe of the air-box device. An additional geometrical configuration of the air-filter box, that includes an internal resonator, obtained through the insertion of inner walls, is considered, too. The effectiveness of the redesigned air-box configurations, are firstly tested in terms of Transmission Loss characteristics, and in terms of gasdynamic noise abatement, as well.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Gasoline direct injection (GDI) engines usually emit higher levels of particulates in warm-up conditions of a driving cycle. Thus, sources of soot formation in these conditions were investigated by measuring particulate numbers (PN) emitted from a single-cylinder GDI engine and their sizes. The combustion was also visualized using an endoscope connected to a high-speed camera. Engine coolant and oil temperatures were varied between 15 and 90<sup>o</sup>C to mimic warm-up conditions. In addition, effects of delaying the start of ignition (SOI) on the emissions in these conditions were examined.</div><div class="htmlview paragraph">Coolant and oil temperatures were varied individually to identify which factor has most effect on PN emissions. While coolant temperature strongly influenced PN with cold oil, the oil temperature insignificantly affected PN at low coolant temperature. These findings indicate that PN emissions are heavily dependent on the engine block’s temperature, which is dominated by the coolant.</div><div class="htmlview paragraph">SOI plays a significant role in PN formation because it influences the wall film thickness on the piston top. In the experimental warm-up conditions, injecting fuel at a later SOI was found to decrease PN emissions. Visualization showed no occurrence of diffusion flames at late SOI timings due to the associated reduction in interaction between liquid fuel and the piston.</div><div class="htmlview paragraph">The integrated luminescence from combustion images was found to correlate closely with PN emission measurements. Thus, higher integrated luminescence, indicating higher soot formation due to pool fires on the piston top, was associated with higher PN levels. When coolant and oil temperatures were both varied, PN emissions were found to decline dramatically with increasing temperatures. At lower temperatures, diffusion combustion occurred on the piston due to persistence of a non-vaporized fuel film. At 15<sup>o</sup>C coolant and oil temperature, this phenomenon was strong, but it gradually declined as the temperature increased. When the temperature reached 60<sup>o</sup>C, diffusion flames started to disappear, resulting in a dramatic decrease in PN.</div></div>

<div class="section abstract"><div class="htmlview paragraph">This paper presents the results of an experimental analysis on a multi-cylinder diesel engine, in which in-cylinder pressure and accelerometer transducers are used with the purpose of developing and setting up a methodology able to monitor and optimize the combustion behavior by means of non-intrusive measurements.</div> <div class="htmlview paragraph">Previously published results have demonstrated the direct relationship existing between in-cylinder pressure and engine block vibration signals, as well as the sensitivity of the engine surface vibration to variation of injection parameters when the accelerometer is placed in sensitive location of the engine block. Moreover, the accelerometer trace has revealed to be able to locate in the crank-angle domain important phenomena characterizing the combustion process (the start of pre-mixed combustion, the crank angle value corresponding to the beginning of diffusive combustion and to the in-cylinder pressure maximum value).</div> <div class="htmlview paragraph">The objective of the present work is to quantify the strict relationship between the in-cylinder pressure signal and the accelerometer trace, in order to obtain information concerning both the pressure maximum value and the pressure rise rate from the accelerometer trace.</div> <div class="htmlview paragraph">In this paper, the previously developed steps of the research program are briefly presented. The processing technique is described and representative results are presented and discussed, in which different values of speed and load have been imposed on the engine.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Many efforts have been invested to improve the fuel efficiency of vehicles mainly for the local consumers. One of the main techniques to have better fuel efficiency is cylinder deactivation system. In this paper, the main research area is focus on the investigation of cylinder deactivation (CDA) technology on common engine part load conditions within common Malaysian driving condition. CDA mostly being applied on multi cylinders engines. It has the advantage in improving fuel consumption by reducing pumping losses at part load engine conditions. Here, the application of CDA on 1.6 liter four cylinders gasoline engine is studied. One-dimensional (1-D) engine modeling is performed to investigate the effect of intake and exhaust valve strategy on engine performance with CDA. The 1-D engine model is constructed starts from the air-box cleaner up to exhaust system according to the 1.6 liter actual engine geometries. The model is simulated at various engine speeds with full load condition. The simulated results show that the constructed model is well correlated to measured data. This correlated model is then used to investigate the effect of valves timing configurations on engine performance. The model is then used to determine the optimum intake and exhaust valve lift and timing for CDA application at part load conditions. Also, the effects on the in-cylinder combustion as well as pumping losses are presented. The study shows that the effects of valves strategies are very significant on the engine performance. Pumping losses is found to be reduced, thus improving fuel consumption and engine thermal efficiency.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The motor generator unit installed on the turbocharger shaft (MGU-H) provides a fundamental contribution to the amazing performances and efficiency of the last Formula 1 power units. The excess of exhaust gas energy - normally dumped through the waste-gate - can be converted into electric energy and used to push the car, by means of a second motor generator unit installed on the engine crankshaft (MGU-K).</div><div class="htmlview paragraph">The goal of this paper is to assess pros and cons of the MGU-H technology when applied to a family of engines of different displacement, installed on a typical passenger car. The influence of engine size and cylinders layout is investigated, under the same set of hypotheses, considering both transient and steady engine operations.</div><div class="htmlview paragraph">The baseline engine is a commercial 2.0 L, SI, 4-cylinder in-line, rated at 200 HP at 4500-5000 rpm. The study considers the following other SI configurations: a) 1.5L, 3-cylinder in-line, 150 HP; b) 3.0L, V6, 300 HP; c) 4.0L, V8, 400 HP; d) 6.0L, V12, 600 HP. It is assumed that all the 5 engines have the same unit displacement and the same maximum load, expressed in terms of brake mean effective pressure as a function of rotational speed.</div><div class="htmlview paragraph">The study is carried out using an experimentally calibrated GT-Power model of the baseline engine, and considering the same class C vehicle. A Matlab/Simulink model is also developed for the analysis of the WLTP driving cycle.</div><div class="htmlview paragraph">The study demonstrates that the MGU-H technology can be conveniently applied to all the considered engines. The maximum advantage in terms of fuel saving on a driving cycle is obtained on the smallest. However, in the V6, V8 and V12 configurations, the installation of one electric turbocharger instead of two, strongly simplifies the engine layout, and it allows the designer to find some space for additional powertrain components, such as electric motors, battery packs, etc. Moreover, the elimination of the turbo-lag problem, gives the designer much more freedom, enabling the adoption of more fuel efficient engine settings.</div></div>