Browse Topic: Exhaust valves
Eaton's decompression engine braking technology for medium and heavy-duty diesel engines delivers high braking power and provides several advantages to the commercial truck owner. Eaton offers rocker arm-based 1 stroke, 1.5 stroke, and 2 stroke systems for overhead cam and cam in block engine architectures. The Compression Release (CR) engine brake avoids overheating and fading of primary friction brake. It reduces or eliminates the need for a driveline retarder. One of the failure modes for Engine Brake (EB) system is excessive lateral displacement of the exhaust valve, caused by non-uniform pressure distribution across the valve during Brake Gas Recirculation (BGR) and Compression Release modes. This excessive deformation is referred to as Valve Wagging. Valve wagging significantly affects the structural stability of the engine brake mechanism. Analyzing its behavior is essential to minimize excessive wear on valve guide and Valve Seat Insert in new designs. Since evaluating the valve wagging phenomenon through prototype testing is both costly and time-consuming, a validated analytical approach was developed. A coupled CFD and structural dynamics analysis approach was developed to predict valve wagging phenomena. This approach includes simulating transient valve motion using a dynamic mesh technique, capturing the influence of valve motion on surrounding flow-field, and assessing the impact of flow field on valve structural displacement. The developed methodology was validated by comparing simulated valve lateral displacement with experimental results, showing good agreement between the two.
This paper presents transient, complex, moving mesh, 3-D CFD analysis of an intebrake lubrication oil circuit for predicting flow performance. Intebrake is a mechanism for improving braking performance during over speeding conditions. The mechanism briefly opens the exhaust valve at the end of a compression stroke with a small valve lift and releases the compressed gases, thereby helping in quick application of the brake. There is no fueling during the process and hence, no combustion induced pressure rise which helps in quick application of the brake. During the intebrake operation, opening of the exhaust valve is achieved by using a complex lube oil circuit inside the exhaust rocker lever. The intebrake lube oil circuit consists of various spring-operated valves with micro-sized clearances, high oil pressure generation up to ~ 250 bar, 3-D movement of the mechanism components, and it is a transient operation. The 3-D movement consists of simultaneous rotational and translational motions with dynamic motions due to net force balance between spring and fluid forces. All these factors make the simulation an absolute need as testing is extremely costly and difficult due to tight space constraints around the mechanism. The 3-D CFD model with automatic intebrake ON and OFF operations makes dynamic mesh motion more complex. In the current work, 3-D CFD simulation approach is developed which can model the intebrake operation by considering dynamic mesh, small clearances, and oil compressibility effects. The predicted intebrake lube system oil pressure is compared with transient, crank angle based test data and the results are found to be in good correlation. This approach has helped in better understanding of the intebrake response to variation of different design parameters and resolving field failures. After a single cylinder intebrake model validation, it has been extended to modeling 6-cylinders and integrated with engine 3-D CFD lube system as well.
In the present work it was studied the flow around the intake and discharge valves of the HONDA CBR 600RR Engine, used in Formula SAE by the team of CEFET-MG, Formula Cefast. Presenting the methodology and experimental results in the measurement of the reversal discharge coefficient of the intake port and the discharge coefficient of exhaust valve of the engine used in the prototype, serving as a starting point for further studies and development of the prototype drive system. These experimental tests were performed on the flow bench infrastructure of the Pontificia Universidade Católica de Minas Gerais, PUC-MG, using the engine head, same model as used in the Formula Cefast team prototype. Necessary parts and adaptations for tests were developed, such as a mechanism for opening and closing the valves during the experiment. Measurements were taken to define the actual mass flow rate of air through the valves for valve lifts, ranging from 0 mm to 7.3 mm for the exhaust valve and from 0 mm to 8.2 mm for the intake valve. The study was performed by opening only one valve. Increment between valve lift measurements was 0.2 mm and 03 measurements were made for each valve lift. From the measurements of the pressure difference before and after the valves and the air temperature it was possible to determine the theoretical mass flow as a function of the valve lift. The ratio between the actual mass flow rate and the theoretical mass flow rate, characterized the discharge coefficient of the flow. The methodology applied in the experiment was effective with a behavior of discharge coefficients as a function of valve lift comparable with other works and theoretical reviews, ranging from 0.45 to 0.91 for the exhaust valve and ranging from 0.42 to 0.69 for the intake valve.
Future Diesel engines must meet extended requirements regarding air-fuel ratio, exhaust gas recirculation (EGR) capability, and tailored exhaust gas temperatures in the complete engine map to comply with the future pollutant emission standards. In this respect, parallel turbines combined with two separate exhaust manifolds have the potential to increase the exhaust gas temperature upstream of the exhaust aftertreatment system and reduce the catalyst light-off time. Furthermore, variable exhaust valve (EV) lifts enable new control strategies of the boosting system without additional actuators. Therefore, hardware robustness can be improved. This article focuses on the parallel-sequential boosting concept (PSBC) for a high-performance four-cylinder Diesel engine with separated exhaust manifolds combined with EV deactivation. One EV per cylinder is connected to one of the separated exhaust manifolds and, thus, connected to one of the turbines. By closing one of the EVs, the corresponding exhaust manifold and the connected turbine are deactivated. The engine operates in mono-turbo mode at low power output. The second turbocharger (TC) blends in as the power requirement increases. A novel design process for complex turbocharging systems is presented, which bases on a validated one-dimensional (1D) gas-exchange simulation model with an advanced TC modelling methodology. The design process handles the high degree of freedom in the layout process with clearly defined optimization steps based on identified system limitations. The modelling of the heat transfer within the TCs has been calibrated with measurement data from a hot gas test bench. This enables an accurate prediction of the exhaust gas temperature upstream of the exhaust aftertreatment system. The designed parallel sequential boosting system demonstrates high potentials in full-load and part-load operation, increasing the exhaust gas temperature downstream of the turbine by up to 40°C at an engine speed of n = 1250 1/min and a brake mean effective pressure of BMEP = 2.7 bar compared to the baseline engine with a serial-sequential boosting concept (SSBC). Furthermore, a higher rate of high-pressure EGR can be generally achieved with that system.
Recent developments in High-Pressure Thermochemical Recuperation technology in the Technion – Israel institute of Technology, were first to allow engines to work on a hydrogen-rich reformate as a stand-alone fuel by its direct injection (DI) to the combustion chamber.This was achieved by using a Magneti Marelli gasoline direct injector, IHP072, modified to enable the gaseous reformate injection. However, this injector , under the used working conditions, suffered from a low flow cross section, non-reliable closure and a non-optimized jet structure, which had a detrimental effect on engine performance. In order to optimize engine performance, i.e. to achieve higher flow rate, shorter open-close timing and higher backward pressure resistance (in the cylinder), an improved injector is needed. In the present work, a novel DI injector was designed producing over expanded reformate jet. One of the main features of the new injector is an outward-opening valve)POPPET valve) with a relatively high flow cross section.Furthermore, a number of elements have been incorporated in the injector design to allow rapid and convenient calibration of the valve lift, sealing force and the magnetic force. Those in turn, enable optimized injector configuration that is well-suited for different working conditions (such as different in-line pressure or flow rates). In this work, the direct-gaseous-injector design process is reported, and its operation is optimized and investigated.
Ever since mainstreaming of automobiles, engineers are focusing on making the vehicles better by means of making them more efficient, powerful and less polluting. In this study, venues of improving low end torque via improvement in volumetric efficiency as well as proper selection of turbochargers is done. An in-depth analysis of gas dynamics with respect to valve timing is studied along with the AVL Boost 1D simulation. It was found that volumetric efficiency starts to improve when there is a reduction in exhaust - exhaust valve overlap. There is an improvement found in the fresh air ratio (lambda) as the residual gas content is reduced. After the selection of valve timing, turbocharger optimization is done with comparison between two turbine sizes. Along with turbocharger comparison, technology comparison is also done namely between normal electronic VGT (Variable Geometry Turbo) (bigger turbine) and electronic VGT coupled with waste gate (smaller turbine). Dynamic as well as static performance is compared on vehicle level as well as testbed level. Time to torque (TTT) value was measured for the turbos and performance was compared for different lambda limits. A MATLAB tool was programmed to predict the vehicle level performance from the TTT values. The performance was validated on vehicle level as well. In summary, better low-end response was observed with smaller turbine size with 5% improvement in low end volumetric efficiency and similar efficiency at rated power.
In order to meet the challenges of future CAFE regulations & pollutant emission, vehicle fuel efficiency must be improved upon without compromising vehicle performance. Optimization of engine breathing & its impact on vehicle level fuel economy, performance needs balance between conflicting requirements of vehicle Fuel Economy, performance & drivability. In this study a Port Fuel Injection, naturally aspirated small passenger car gasoline engine was selected which was being used in a typical small passenger car. Simulation approach was used to investigate vehicle fuel economy and performance, where-in 1D CFD Engine model was used to investigate and optimize Valve train events (Intake and exhaust valve open and close timings) for best fuel economy. Engine Simulation software is physics based and uses a phenomenological approach 0-D turbulent combustion model to calculate engine performance parameters. Engine simulation model was calibrated within 95% accuracy of test data. This model is sufficient to analyze the change in engine performance with change of valve timings. GT POWER engine model was integrated to a vehicle simulation model of small hatchback car developed using GT Drive and validated for regulatory drive cycle. 1-D simulation model was run for various combination of Intake and exhaust valve timings. Impact of individually changing each valve timing on Fuel Economy was assessed initially via Vehicle simulation model. Optimization of valve timings was carried out and after analysis Atkinson effect was observed at final timing position. Intake valve closing was delayed which reduced compression stroke. This reduced pumping effort at F.E relevant engine operating points and improved fuel consumption. Fuel economy of optimized proposal was validated against test vehicle. It was possible to fix a Non-Variable Valve Timing (VVT) Valve train without extensive hardware trials for desired performance.
The partnership for advancing combustion engines (PACE) is a US Department of Energy consortium involving multiple national laboratories and includes a goal of addressing key efficiency and emission barriers in light-duty engines fueled with a market-representative E10 gasoline. A major pillar of the initiative is the generation of detailed experimental data and modeling capabilities to understand and predict cold-start behavior. Cold-start, as defined by the time between first engine crank and three-way catalyst light-off, is responsible for a large percentage of NOx, unburned hydrocarbon and particulate matter emissions in light-duty engines. Minimizing emissions during cold-start is a trade-off between achieving faster light-off of the three-way catalyst and engine out emissions during that period. In this study, gaseous and soot emissions were measured at a distance representative of the three-way catalyst position downstream of the engine at a 2 bar net indicated mean effective pressure (NIMEP) steady-state operating condition representative of cold-start. The test matrix included sweeps of ignition timing 15 degrees-before to 10 degrees-after top dead center firing (TDCf) across three different spark-plug heat dispersal ranges (HR). Additionally, the effect of varying exhaust valve opening (EVO) timing on combustion stability and emissions was also studied. Results show that the spark plug HR affects the coefficient of variation (COV) of NIMEP under all cold-start conditions, while the impact on emissions was found to be minimal. At very retarded spark timings, colder spark plugs required higher air and fuel flow to maintain the desired 2bar NIMEP load, but the fraction of fuel energy going into the exhaust was found to be similar for all spark plugs. Retarding exhaust valve timings showed a simultaneous reduction in emissions while increasing the fraction of fuel energy being fed into the exhaust. However, engine COV was also observed to increase with retarded exhaust timings.
Despite a long history of development, modern spark-ignition (SI) engines are still restricted in obtaining higher thermal efficiency and better performance by knock. Knocking combustion is an abnormal combustion phenomenon caused by the autoignition of unburned air-fuel mixture ahead of the propagating flame front. This work describes investigations into the significance of spark plug location (with respect to inlet and exhaust valve position) on the knock formation mechanism. To facilitate the investigation, four spark plugs were installed in a specialized liner at four equispaced distinct locations to propagate flames from those locations, which provoked a distinct flame propagation from each and thus individual autoignition profiles. Six pressure transducers were arranged to precisely record the pressure oscillations, knock intensities, and combustion characteristics. Four of the six transducers were mounted on the circumference of the liner (each next to one of the spark plugs), one was placed at the center of the cylinder head, and one at a slight offset from the center of cylinder head. The results showed that the spark plug which was close to the exhaust valves triggered higher knock intensity along with earlier CA50, but the spark plug near the inlet valves caused weaker knock intensities for the same operating conditions. In addition, the study also covered the effect of swirl direction to suppress knock. A band pass filtering analysis was applied to estimate the pressure oscillations with respect to the spark plug locations, using data from the multiple pressure sensors. Furthermore, Fast Fourier Transform (FFT) analyses were implemented to estimate the frequency of the pressure oscillation resulting from knock. It was found that firing the spark plugs, near the inlet and between the inlet and exhaust valves promoted the (1, 0) acoustic mode effectively, while the spark plug near the exhaust valves caused the (1, 0) mode along with the (2, 0) acoustic mode for the same operating conditions, indicating that the autoignition was initiated near the cylinder walls.
The introduction of real driving emissions cycles and increasingly restrictive emissions regulations force the automotive industry to develop new and more efficient solutions for emission reductions. In particular, the cold start and catalyst heating conditions are crucial for modern cars because is when most of the emissions are produced. One interesting strategy to reduce the time required for catalyst heating is post-oxidation. It consists in operating the engine with a rich in-cylinder mixture and completing the oxidation of fuel inside the exhaust manifold. The result is an increase in temperature and enthalpy of the gases in the exhaust, therefore heating the three-way-catalyst. The following investigation focuses on the implementation of post-oxidation by means of scavenging in a four-cylinder, turbocharged, direct injection spark ignition engine. The investigation is based on detailed measurements that are carried out at the test-bench. Due to the complexity of the investigated phenomenon, the analysis at the test-bench has been sustained by 3D-CFD simulations. At first a 3D-CFD full-engine model has been implemented to reproduce the complete engine from the air-box up to the turbine inlet. This model is able to simulate all the relevant full-engine effects like scavenging, cylinder-to-cylinder interaction and local inhomogeneity inside the cylinder. The second implemented model focuses on the exhaust manifold, from the exhaust valve up to the turbine volute, and it is characterized by a fine computational grid and by the implementation of a chemical reaction mechanism. Both models have been validated using the detailed measurements of the test-bench. The simulation matched precisely the measurements and enabled a better interpretation of experimental data. The simulation methodology has been applied also to other engine operating points enabling a mapping of post-oxidation, the development of a post-oxidation model for 1D engine simulation and the implementation of a simplified model for the full-engine simulation.
Pre-chamber combustion (PCC) engines allow extending the lean limit of operation compared to common SI engines, thus being a candidate concept for the future clean transportation targets. To understand the fundamental mechanisms of the main chamber charge ignition in PCC engines, the effects of the composition in the pre-chamber were investigated numerically. A well-stirred reactor combustion model coupled with a methane oxidation mechanism reduced from GRI 3.0 was used. An open-cycle simulation was run with initialization at exhaust valve opening (EVO). For posterior simulations, the initial flow field was attained by mapping the field variables obtained from the full cycle simulation. The entire simulation domain (pre-chamber and main chamber) global excess air ratio (λ) was set to 1.3. As parametric variants, additional amounts of fuel were further injected into the pre-chamber to achieve a global pre-chamber λ of 0.7 and 1.0 at spark timing, thus having the pre-chamber and the main chamber with different compositions (emulating an active type pre-chamber). For the same operating conditions, the pre-chamber charge residence time after the spark ignition is mostly governed by the geometry. Therefore, by varying the air/fuel ratio (AFR) in the pre-chamber, it is possible to produce jets with various compositions and ultimately determine the impact of the pre-chamber enrichment on the main chamber response. The results show that the pre-chamber is sensitive to fuel enrichment and the results serve as a baseline guideline for subsequent studies.
This paper presents analytical research conducted into the level of fuel consumption improvement that can be expected from turbocompounding a medium-duty opposed-piston 2-stroke engine, which is part of a hybridized vehicle propulsion system. It draws on a successful earlier study which showed a non-compounded opposed-piston engine to be clearly superior to other forms of 2-stroke engine, such as the widely adopted uniflow-scavenged poppet valve configuration. Electrical power transmission is proposed as the method of providing the necessary variable-speed drive to transmit excess turbine power to the system energy storage medium. The work employs one-dimensional engine simulation on a single-cylinder basis, using brake specific fuel consumption (BSFC) as the reportable metric, coupled with positive or negative power flow to the engine from the compounder; this is a variation on an approach successfully used in earlier work. Here it shows the sensitivities of the overall system to cylinder pressure, the compressor and turbine efficiencies, exhaust backpressure and also provides a means to investigate the effect of the power transmission efficiency on the overall benefit. Reheating the air before the turbine is also investigated as a means of providing a “burst” performance facility, albeit at the expense of extra fuel consumption. Positive compounding work is shown to be achievable across all investigated engine operating points under certain conditions. Operating points at lower engine speeds showed an increased propensity for turbocompounding, with 5-6% of the brake torque arising from the compounder, compared to those at higher engine speeds, where a maximum of 4% was seen. BSFC was found to be highly dependent on compounding torque with improvements only arising from reducing backpressure. A better understanding of the flow restrictions of the exhaust aftertreatment and muffler systems, for a given application, would allow for more accurate determination of the possibility for BSFC reduction within realistic operating conditions.
This paper shows the potential benefits of implementing four configurations of reed valves at the inlet of the two-stroke compressor used in the double compression expansion engine (DCEE) concept or 8-stroke engines over the conventional poppet valves used in 4-stroke internal combustion engines. To model the reed and poppet valve configurations, the discharge coefficient was estimated from RANS computational fluid dynamics simulations using ANSYS Fluent 2020 R1, with a pressure difference up to 0.099 bar. The calculated discharge coefficients for each case were then fed in a zero-one dimension model using GT-Power to understand the valve performance i.e. the volumetric efficiency of the compressor cylinder and the mean indicated pressure during the compression process at 1200 rpm. The results showed that for reed valve configurations, the discharge coefficient and mass flow rate were higher, the pressure drop was lower and the response with negative pressure difference was faster compared to poppet valves. In addition, all the reed valve cases showed improvement in volumetric efficiency and a drop in mean effective pressure than poppet valves. In particular, the optimum reed valve geometry in the present study resulted in a volumetric efficiency improvement of 7.2 percentage points and a mean effective pressure reduction of 3.2 percentage points compared to conventional poppet valves.
Exhaust sensors and actuators used in automotive applications are subjected to wide variety of operating ambient conditions , the performance of these actuators is challenging especially at cold ambient operating conditions, active exhaust tuning valves with position sensors are used to adjust the sound levels, or noise, vibration and harshness (NVH) from a control unit within the vehicle that leads to an improved driving experience wherein the driver selects their preferred sound levels. However, the operating behavior is crucially influenced by the characteristics of the drive cycle and ambient temperature. The study in this paper is intended to evaluate the icing formation at the start of drive cycle and at different ambient temperature conditions. The test data were obtained through real road and chassis dyno testing at different ambient conditions. The results of the testing indicated that a drive cycle with low engine speed and engine load, like a typical city road and cold ambient temperatures, had a low probability of successful operation of active exhaust valves. However, information reported from the actuator could be used along with other engine parameters to evaluate the performance of the system. In this study, an example of how the water collected in the exhaust system on gasoline only powertrain impacts the performance of the exhaust tuning valve is discussed. Root cause analysis is provided, noise factors of valve freezing is also evaluated, control software strategy is presented with vehicle validation results.
For the regeneration of the Lean NOx Trap (LNT) a rich air-to-fuel ratio must be generated. This operation is very critical and has low combustion stability, especially in low load operation. A certain minimum engine load is always required for the regeneration phase. In the Real Driving Emissions this minimum engine load can be undercut over a long period of time. Hence, a reliable regeneration phase is not possible. The aim of these investigations is to extend the engine map range in which regeneration is possible towards lower loads. This is done by means of a variable valve train with second exhaust valve lift, which increases the internal residual gas amount. This in turns increases the temperature at start of combustion in the cylinder. Especially at low load and low combustion stability this leads to a stabilization of the combustion process. This advantage in combustion stability can be used for a reduction of the minimum engine load. The approach of this work consists of investigations on the engine test bench and accompanying simulations. The combustion process is thermodynamically examined and evaluated on the engine test bench using pressure trace and gas exchange analysis, including a residual gas model.
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