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Author: Yangtao Li
Publisher:
ISBN:
Category : Automobiles
Languages : en
Pages : 121
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Book Description
Variety of technologies along with the mechanisms for their implementations have been developed in order to pursue possible improvements in the performance and efficiency of gasoline engines. Yet, most of the commonly used techniques, such as the cam-based variable valve timings (VVT) and variable compression ratio (VCR), are realized by different kinds of complicated mechanisms, providing an extended but still relatively limited adjustability, for attaining improved valve timings and different engine cycles according to the varying working conditions of the engine. The hydraulic variable valve actuation (HVVA) system, however, can provide greater freedoms to the engine valve motions than most of the traditional cam-based valve train systems do. By considering the characteristics of the HVVA system, the strategies of putting its outstanding flexibilities into use for further improving the performances of gasoline engines with respect to power and fuel economy are developed in this research. By utilizing the flexibility offered by the HVVA system, a set of new valve motion strategies is developed for realizing an unthrottled engine load control. In this research, the late exhaust valve closure (LEVC) and early intake valve closure (EIVC) strategies are adopted at the same time for granting the engine an internal exhaust gas recirculation (IEGR) feature and together evolved into a tunable IEGR scheme for fulfilling the partial engine loads without throttling. Alternatively, the realization to the proposed variable Atkinson cycle (VAC), which is realized by late intake valve closures (LIVCs), can also achieve the same goal of unthrottled engine load control for partial load operations. Moreover, an HVVA engine model is proposed and built in GT-suite, which is able to capture the interdependencies of the HVVA system and the engine operations, and is as well carefully calibrated by experimental data acquired from individual bench tests of the HVVA system and the baseline engine. The HVVA engine in this research is a converted from a baseline single-cylinder engine and is able to carry out a variable Otto cycle (VOC) at full engine load operations for achieving higher power performance while realizing a variable Atkinson cycle (VAC) or a tunable IEGR feature at partial engine load operations for gaining better fuel economy without having any further modifications or attaching additional components to the engine. In addition, a set of genetic algorithm (GA)-based optimization schemes is also developed for identifying the proper operating parameters of the HVVA engine when adopting any of the proposed engine operation schemes. A MATLAB-Simulink and GT-Suite coupling simulation structure is proposed for carrying out the GA approaches. Furthermore, these GA optimizers are designed to be capable of maintaining their proper functionality while non-linear constraints are taken into considerations. By running the HVVA engine with the optimized operating parameters identified by the proposed GA optimizations, noticeable improvements on the engine outputs at full load operations and fuel economy at partial load operations are revealed. Benefited from the features of the HVVA system, the tunings of the HVVA engine can be flexibly customized to fulfill any requirements towards different desired engine characteristics. At last, with the corresponding operating parameters be optimized by the proposed GA optimization techniques, all the proposed HVVA valve motion strategies are carried out by an actual prototype HVVA engine and are qualitatively validated by experiments. The experimental results are showing expected outcomes on the improvements to the engine's power and fuel economy performances under corresponding operations. A power improvement of 12.3% is noticed from the experiments by running the HVVA engine in the proposed VOC operation at the exemplary 1000rpm engine speed. In addition, comparing to the throttled operation of the baseline engine, the experiment studies show also the HVVA engine is able to run with leaner air-fuel mixtures to achieve the same desired partial engine load operations by adopting the IEGR scheme or the VAC operation. With an adopted air-fuel ratio (AFR) of 16.1 for the IEGR scheme and 16.3 for the VAC scheme, the engine could realize the same exemplary speed-load operation of 1000rpm/5.2Nm, while the baseline engine with throttling load control requires an AFR of 14.7 to achieve the same partial load operation.
Author: Yangtao Li
Publisher:
ISBN:
Category : Automobiles
Languages : en
Pages : 121
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Book Description
Variety of technologies along with the mechanisms for their implementations have been developed in order to pursue possible improvements in the performance and efficiency of gasoline engines. Yet, most of the commonly used techniques, such as the cam-based variable valve timings (VVT) and variable compression ratio (VCR), are realized by different kinds of complicated mechanisms, providing an extended but still relatively limited adjustability, for attaining improved valve timings and different engine cycles according to the varying working conditions of the engine. The hydraulic variable valve actuation (HVVA) system, however, can provide greater freedoms to the engine valve motions than most of the traditional cam-based valve train systems do. By considering the characteristics of the HVVA system, the strategies of putting its outstanding flexibilities into use for further improving the performances of gasoline engines with respect to power and fuel economy are developed in this research. By utilizing the flexibility offered by the HVVA system, a set of new valve motion strategies is developed for realizing an unthrottled engine load control. In this research, the late exhaust valve closure (LEVC) and early intake valve closure (EIVC) strategies are adopted at the same time for granting the engine an internal exhaust gas recirculation (IEGR) feature and together evolved into a tunable IEGR scheme for fulfilling the partial engine loads without throttling. Alternatively, the realization to the proposed variable Atkinson cycle (VAC), which is realized by late intake valve closures (LIVCs), can also achieve the same goal of unthrottled engine load control for partial load operations. Moreover, an HVVA engine model is proposed and built in GT-suite, which is able to capture the interdependencies of the HVVA system and the engine operations, and is as well carefully calibrated by experimental data acquired from individual bench tests of the HVVA system and the baseline engine. The HVVA engine in this research is a converted from a baseline single-cylinder engine and is able to carry out a variable Otto cycle (VOC) at full engine load operations for achieving higher power performance while realizing a variable Atkinson cycle (VAC) or a tunable IEGR feature at partial engine load operations for gaining better fuel economy without having any further modifications or attaching additional components to the engine. In addition, a set of genetic algorithm (GA)-based optimization schemes is also developed for identifying the proper operating parameters of the HVVA engine when adopting any of the proposed engine operation schemes. A MATLAB-Simulink and GT-Suite coupling simulation structure is proposed for carrying out the GA approaches. Furthermore, these GA optimizers are designed to be capable of maintaining their proper functionality while non-linear constraints are taken into considerations. By running the HVVA engine with the optimized operating parameters identified by the proposed GA optimizations, noticeable improvements on the engine outputs at full load operations and fuel economy at partial load operations are revealed. Benefited from the features of the HVVA system, the tunings of the HVVA engine can be flexibly customized to fulfill any requirements towards different desired engine characteristics. At last, with the corresponding operating parameters be optimized by the proposed GA optimization techniques, all the proposed HVVA valve motion strategies are carried out by an actual prototype HVVA engine and are qualitatively validated by experiments. The experimental results are showing expected outcomes on the improvements to the engine's power and fuel economy performances under corresponding operations. A power improvement of 12.3% is noticed from the experiments by running the HVVA engine in the proposed VOC operation at the exemplary 1000rpm engine speed. In addition, comparing to the throttled operation of the baseline engine, the experiment studies show also the HVVA engine is able to run with leaner air-fuel mixtures to achieve the same desired partial engine load operations by adopting the IEGR scheme or the VAC operation. With an adopted air-fuel ratio (AFR) of 16.1 for the IEGR scheme and 16.3 for the VAC scheme, the engine could realize the same exemplary speed-load operation of 1000rpm/5.2Nm, while the baseline engine with throttling load control requires an AFR of 14.7 to achieve the same partial load operation.
Author:
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ISBN:
Category :
Languages : en
Pages :
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Abstract : Recent fuel economy and emission regulations are the major concern of the research and development of modern internal combustion engine. Such technologies include variable valve timing (VVT), direct injection (DI), turbocharging, downsizing, and over-expanded cycle are used by many manufacturers to improve engine fuel economy or increase power density. Current Atkinson cycle technology in the production engine is mainly realized by an advanced valvetrain system to reduce the effective compression ratio while maintaining the same expansion ratio. Another approach to realize over-expanded cycle engine is to utilize a multi-link cranktrain mechanism. Although the Atkinson cycle was originally patented in the 1880s, the research of the over-expanded cycle engine realized by a multi-link cranktrain design is incomplete. This study focuses on the investigation of over-expanded engine realized by a cranktrain with a multi-link mechanism. The multi-link mechanism of cranktrain was developed and simulated with the constraints of packaging and match the same specification as the baseline engine including compression ratio, bore, and intake/compression stroke. This study also discusses adapting the cam profiles, cam phasing, and spark timing to compensate for the geometric characteristics difference between an Atkinson cycle engine and a conventional engine. The 1-D engine model was developed and calibrated in the commercial engine program, GT-Suite/GT-Power, based on the experimental results from a production four-cylinder spark-ignited engine (not over-expanded). The simulations of multi-link over-expanded engine and high compression engine were realized by substituting the new cranktrain for the baseline cranktrain In this study, the investigation of the multi-link over-expanded engine included a series of operating conditions from light load to high load. The results were compared at the optimized condition between the baseline engine, multi-link over-expand engine, and high compression engine. At the light load condition, it was observed that the net indicated efficiency of the over-expanded engine was slightly improved based on the adjustment method. This study also investigated the operating condition of the baseline engine with knock constrained and exhaust temperature constrained conditions at medium to high load. With the optimization, the over-expanded cycle engine is less constrained than the baseline engine due to the reduced knock propensity and exhaust gas temperature resulting in the further improvement of net indicated efficiency. The study of the multi-link over-expanded cycle engine includes the comparison with the latest production high compression ratio engine, representing state-of-the-art high efficiency engine technologies. The net indicated efficiency of multi-link over-expanded engine is even better than the peak efficiency point of the high compression engine.
Author: Hsien-Hsin Liao
Publisher: Stanford University
ISBN:
Category :
Languages : en
Pages : 201
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There has been an enormous global research effort to alleviate the current and projected environmental consequences incurred by internal combustion (IC) engines, the dominant propulsion systems in ground vehicles. Two technologies have the potential to improve the efficiency and emissions of IC engines in the near future: variable valve actuation (VVA) and homogeneous charge compression ignition (HCCI). IC engines equipped with VVA systems are proven to show better performance by adjusting the valve lift and timing appropriately. An electro-hydraulic valve system (EHVS) is a type of VVA system that possesses full flexibility, i.e., the ability to change the valve lift and timing independently and continuously, making it an ideal rapid prototyping tool in a research environment. Unfortunately, an EHVS typically shows a significant response time delay that limits the achievable closed-loop bandwidth and, as a result, shows poor tracking performance. In this thesis, a control framework that includes system identification, feedback control design, and repetitive control design is presented. The combined control law shows excellent performance with a root-mean-square tracking error below 40 [Mu]m over a maximum valve lift of 4 mm. A stability analysis is also provided to show that the mean tracking error converges to zero asymptotically with the combined control law. HCCI, the other technology presented in this thesis, is a combustion strategy initiated by compressing a homogeneous air-fuel mixture to auto-ignition, therefore, ignition occurs at multiple points inside the cylinder without noticeable flame propagation. The result is rapid combustion with low peak in-cylinder temperature, which gives HCCI improved efficiency and reduces NOx formation. To initiate HCCI with a typical compression ratio, the sensible energy of the mixture needs to be high compared to a spark ignited (SI) strategy. One approach to achieve this, called recompression HCCI, is by closing the exhaust valve early to trap a portion of the exhaust gas in the cylinder. Unlike a SI or Diesel strategy, HCCI lacks an explicit combustion trigger, as autoignition is governed by chemical kinetics. Therefore, the thermo-chemical conditions of the air-fuel mixture need to be carefully controlled for HCCI to occur at the desired timing. Compounding this challenge in recompression HCCI is the re-utilization of the exhaust gas which creates cycle-to-cycle coupling. Furthermore, the coupling characteristics can change drastically around different operating points, making combustion timing control difficult across a wide range of conditions. In this thesis, a graphical analysis examines the in-cylinder temperature dynamics of recompression HCCI and reveals three qualitative types of temperature dynamics. With this insight, a switching linear model is formulated by combining three linear models: one for each of the three types of temperature dynamics. A switching controller that is composed of three local linear feedback controllers can then be designed based on the switching model. This switching model/control formulation is tested on an experimental HCCI testbed and shows good performance in controlling the combustion timing across a wide range. A semi-definite program is formulated to find a Lyapunov function for the switching model/control framework and shows that it is stable. As HCCI is dictated by the in-cylinder thermo-chemical conditions, there are further concerns about the robustness of HCCI, i.e., the boundedness of the thermo-chemical conditions with uncertainty existing in the ambient conditions and in the engine's own characteristics due to aging. To assess HCCI's robustness, this thesis presents a linear parameter varying (LPV) model that captures the dynamics of recompression HCCI and possesses an elegant model structure that is more amenable to analysis. Based on this model, a recursive algorithm using convex optimization is formulated to generate analytical statements about the boundedness of the in-cylinder thermo-chemical conditions. The bounds generated by the algorithm are also shown to relate well to the data from the experimental testbed.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 512
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Low Temperature Combustion (LTC) Strategies such as Reactivity Controlled Compression Ignition (RCCI) are highly sensitive to intake conditions, which are influenced by the gas exchange process. Because the gas exchange process is dependent on air handling system characteristics, optimizing the air handling system for improved RCCI engine performance is necessary. Major objectives were: 1. Improve combustion efficiency while mitigating unburnt hydrocarbon (UHC) and carbon monoxide (CO) emissions at low load, 2. Determine system parameters and configurations for high loads and 3. Examine variable valve actuation (VVA) and manifold redesign to maximize fuel efficiency. Zero-dimensional, one-dimensional and multi-dimensional models were used in this simulation study. Early Exhaust Valve Opening (EEVO) using fully flexible variable valvetrains and cam-phasers, and cylinder deactivation were evaluated for their impact on aftertreatment efficiency and fuel economy at low load. For near-idle conditions, cylinder deactivation in which only one cylinder was fired gave the best fuel economy and catalyst efficiency. For the second objective of performing high load system simulation, a low pressure (LP) EGR circuit was incorporated into the engine model. High Pressure EGR could not be used for high loads as the pre-turbine pressure was insufficient to drive EGR flow. Moreover, insufficient exhaust energy would be available to the turbine, resulting in lower boost pressures. For the final objective, the stock exhaust manifold was redesigned using the Divided Exhaust Period (DEP) concept by splitting it into two manifolds, one connected to each exhaust valve. By using VVA to separately actuate the valves, overlap between the valves was varied, changing the exhaust distribution between the two manifolds, and thereby regulating boost pressure. With DEP, due to lower overall backpressures, pumping penalty decreased, but the pumping benefit was negated by parasitic losses from the supercharger which had to compensate for the boost deficit. Replacing the fixed geometry turbocharger with a variable geometry turbocharger (VGT) improved the Brake Specific Fuel Consumption (BSFC) over the base engine by 1%, while bypassing the turbine at low load gave elevated exhaust gas temperatures for thermal management.
Author:
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Category :
Languages : en
Pages :
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The primary objective of this project was to develop a true Flex Fuel Vehicle capable of running on any blend of ethanol from 0 to 85% with reduced penalty in usable vehicle range. A research and development program, targeting 10% improvement in fuel economy using a direct injection (DI) turbocharged spark ignition engine was conducted. In this project a gasoline-optimized high-technology engine was considered and the hardware and configuration modifications were defined for the engine, fueling system, and air path. Combined with a novel engine control strategy, control software, and calibration this resulted in a highly efficient and clean FFV concept. It was also intended to develop robust detection schemes of the ethanol content in the fuel integrated with adaptive control algorithms for optimized turbocharged direct injection engine combustion. The approach relies heavily on software-based adaptation and optimization striving for minimal modifications to the gasoline-optimized engine hardware system. Our ultimate objective was to develop a compact control methodology that takes advantage of any ethanol-based fuel mixture and not compromise the engine performance under gasoline operation.
Author: National Research Council
Publisher: National Academies Press
ISBN: 0309216389
Category : Science
Languages : en
Pages : 373
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Various combinations of commercially available technologies could greatly reduce fuel consumption in passenger cars, sport-utility vehicles, minivans, and other light-duty vehicles without compromising vehicle performance or safety. Assessment of Technologies for Improving Light Duty Vehicle Fuel Economy estimates the potential fuel savings and costs to consumers of available technology combinations for three types of engines: spark-ignition gasoline, compression-ignition diesel, and hybrid. According to its estimates, adopting the full combination of improved technologies in medium and large cars and pickup trucks with spark-ignition engines could reduce fuel consumption by 29 percent at an additional cost of $2,200 to the consumer. Replacing spark-ignition engines with diesel engines and components would yield fuel savings of about 37 percent at an added cost of approximately $5,900 per vehicle, and replacing spark-ignition engines with hybrid engines and components would reduce fuel consumption by 43 percent at an increase of $6,000 per vehicle. The book focuses on fuel consumption-the amount of fuel consumed in a given driving distance-because energy savings are directly related to the amount of fuel used. In contrast, fuel economy measures how far a vehicle will travel with a gallon of fuel. Because fuel consumption data indicate money saved on fuel purchases and reductions in carbon dioxide emissions, the book finds that vehicle stickers should provide consumers with fuel consumption data in addition to fuel economy information.
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Category :
Languages : en
Pages :
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The central objective of the proposed work is to demonstrate an HCCI (homogeneous charge compression ignition) capable SI (spark ignited) engine that is capable of fast and smooth mode transition between SI and HCCI combustion modes. The model-based control technique was used to develop and validate the proposed control strategy for the fast and smooth combustion mode transition based upon the developed control-oriented engine; and an HCCI capable SI engine was designed and constructed using production ready two-step valve-train with electrical variable valve timing actuating system. Finally, smooth combustion mode transition was demonstrated on a metal engine within eight engine cycles. The Chrysler turbocharged 2.0L I4 direct injection engine was selected as the base engine for the project and the engine was modified to fit the two-step valve with electrical variable valve timing actuating system. To develop the model-based control strategy for stable HCCI combustion and smooth combustion mode transition between SI and HCCI combustion, a control-oriented real-time engine model was developed and implemented into the MSU HIL (hardware-in-the-loop) simulation environment. The developed model was used to study the engine actuating system requirement for the smooth and fast combustion mode transition and to develop the proposed mode transition control strategy. Finally, a single cylinder optical engine was designed and fabricated for studying the HCCI combustion characteristics. Optical engine combustion tests were conducted in both SI and HCCI combustion modes and the test results were used to calibrate the developed control-oriented engine model. Intensive GT-Power simulations were conducted to determine the optimal valve lift (high and low) and the cam phasing range. Delphi was selected to be the supplier for the two-step valve-train and Denso to be the electrical variable valve timing system supplier. A test bench was constructed to develop control strategies for the electrical variable valve timing (VVT) actuating system and satisfactory electrical VVT responses were obtained. Target engine control system was designed and fabricated at MSU for both single-cylinder optical and multi-cylinder metal engines. Finally, the developed control-oriented engine model was successfully implemented into the HIL simulation environment. The Chrysler 2.0L I4 DI engine was modified to fit the two-step vale with electrical variable valve timing actuating system. A used prototype engine was used as the base engine and the cylinder head was modified for the two-step valve with electrical VVT actuating system. Engine validation tests indicated that cylinder #3 has very high blow-by and it cannot be reduced with new pistons and rings. Due to the time constraint, it was decided to convert the four-cylinder engine into a single cylinder engine by blocking both intake and exhaust ports of the unused cylinders. The model-based combustion mode transition control algorithm was developed in the MSU HIL simulation environment and the Simulink based control strategy was implemented into the target engine controller. With both single-cylinder metal engine and control strategy ready, stable HCCI combustion was achived with COV of 2.1% Motoring tests were conducted to validate the actuator transient operations including valve lift, electrical variable valve timing, electronic throttle, multiple spark and injection controls. After the actuator operations were confirmed, 15-cycle smooth combustion mode transition from SI to HCCI combustion was achieved; and fast 8-cycle smooth combustion mode transition followed. With a fast electrical variable valve timing actuator, the number of engine cycles required for mode transition can be reduced down to five. It was also found that the combustion mode transition is sensitive to the charge air and engine coolant temperatures and regulating the corresponding temperatures to the target levels during the combustion mode transition is the key for a smooth combustion mode transition. As a summary, the proposed combustion mode transition strategy using the hybrid combustion mode that starts with the SI combustion and ends with the HCCI combustion was experimentally validated on a metal engine. The proposed model-based control approach made it possible to complete the SI-HCCI combustion mode transition within eight engine cycles utilizing the well controlled hybrid combustion mode. Without intensive control-oriented engine modeling and HIL simulation study of using the hybrid combustion mode during the mode transition, it would be impossible to validate the proposed combustion mode transition strategy in a very short period.
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Category :
Languages : en
Pages :
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The first phase of the project consists of four months of applied research, starting from September 1, 2005 and was completed by December 31, 2005. During this time, the project team heavily relied on highly detailed numerical modeling techniques to evaluate the feasibility of the APA technology. Specifically, (i) A GT-Power{sup TM}engine simulation model was constructed to predict engine efficiency at various operating conditions. Efficiency was defined based on the second-law thermodynamic availability. (ii) The engine efficiency map generated by the engine simulation was then fed into a simplified vehicle model, which was constructed in the Matlab/Simulink environment, to predict fuel consumption of a refuse truck on a simple collection cycle. (iii) Design and analysis work supporting the concept of retrofitting an existing Sturman Industries Hydraulic Valve Actuation (HVA) system with the modifications that are required to run the HVA system with Air Power Assist functionality. A Matlab/Simulink model was used to calculate the dynamic response of the HVA system. Computer aided design (CAD) was done in Solidworks for mechanical design and hydraulic layout. At the end of Phase I, 11% fuel economy improvement was predicted. During Phase II, the engine simulation group completed the engine mapping work. The air handling group made substantial progress in identifying suppliers and conducting 3D modelling design. Sturman Industries completed design modification of the HVA system, which was reviewed and accepted by Volvo Powertrain. In Phase II, the possibility of 15% fuel economy improvement was shown with new EGR cooler design by reducing EGR cooler outlet temperature with APA engine technology from Air Handling Group. In addition, Vehicle Simulation with APA technology estimated 4 -21% fuel economy improvement over a wide range of driving cycles. During Phase III, the engine experimental setup was initiated at VPTNA, Hagerstown, MD. Air Handling system and HVA system were delivered to VPTNA and then assembly of APA engine was completed by June 2007. Functional testing of APA engine was performed and AC and AM modes testing were completed by October 2007. After completing testing, data analysis and post processing were performed. Especially, the models were instrumental in identifying some of the key issues with the experimental HVA system. Based upon the available engine test results during AC and AM modes, the projected fuel economy improvement over the NY composite cycle is 14.7%. This is close to but slightly lower than the originally estimated 18% from ADVISOR simulation. The APA project group demonstrated the concept of APA technology by using simulation and experimental testing. However, there are still exists of technical challenges to meet the original expectation of APA technology. The enabling technology of this concept, i.e. a fully flexible valve actuation system that can handle high back pressure from the exhaust manifold is identified as one of the major technical challenges for realizing the APA concept.
Author: Halim Gustiono Santoso
Publisher:
ISBN:
Category :
Languages : en
Pages : 130
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Gasoline Homogeneous Charge Compression Ignition (HCCI) engine has the potential of providing better fuel economy and emissions characteristics than current spark ignition engines. One implementation of this technology employs a Variable Valve Timing (VVT) system and is also often referred to as Controlled Auto Ignition (CAI) combustion in the literature. The objective of the study can be divided into two topics. First, the dynamic nature of load trajectory and several important phenomena in CAI mode were investigated. Second, the issues encountered during mode transition between SI and CAI regime were considered. Despite wide-open-throttle operation, pumping loss in CAI mode was not negligible. A major source of pumping loss in CAI mode was the heat transfer to cylinder wall during the recompression process due to the high in-cylinder residual gas temperature. The influence of fuel air equivalence ratio on combustion stability was analyzed to explain the misfires phenomenon in fuel rich condition during transient operation. Heat release analysis has been conducted to characterize the combustion process in CAI mode. Large variations of the 50% burned point due to fluctuation of residual gas mass and temperature were observed. Small step changes in valve timings (EVC, EVO, and IVC) and fueling resulted in a new steady state within 3-4 engine cycles at 1500 rpm. These small step changes are reversible in nature. Sudden large step change in load required much longer time to reach steady state due to the time required for thermal stabilization. Misfires were observed in large low-load-to-high-load step change but not in high-load-to-low-load step change.
Author: Theodore Taylor
Publisher:
ISBN:
Category : Automobiles
Languages : en
Pages : 96
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