Effects of Negative Valve Overlap on HCCI Combustion and Its Use in the Control of HCCI Combustion Timing PDF Download
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Author: Alexander E. Schramm Publisher: ISBN: Category : Automobiles Languages : en Pages : 114
Book Description
Homogeneous charge compression ignition (HCCI) combustion can produce higher efficiencies and lower emissions when compared to tradition spark or compression ignition engines. This study reports an experimental investigation into the effects of valve timings on HCCI combustion conditions. Using a single cylinder engine with state-of-the-art electromagnetic variable valve timing (EVVT) fully independent valves, a series of tests are conducted with varying negative valve overlap (NVO). The in-cylinder residual trapped by the NVO causes an advance in combustion timing, a shortening of burn duration as well as increase in load and increase in brake specific fuel consumption. Asymmetric valve timings are also investigated and show complex behavior with high sensitivity of combustion timing in certain operating ranges. Finally, these strategies are implemented as a set of feedback controllers including a proportional-integral (PI) controller and a feedforward with integral action controller. Both controllers have good tracking for step changes in combustion timing setpoint with the feedforward controller providing a rise time of just four cycles.
Author: Alexander E. Schramm Publisher: ISBN: Category : Automobiles Languages : en Pages : 114
Book Description
Homogeneous charge compression ignition (HCCI) combustion can produce higher efficiencies and lower emissions when compared to tradition spark or compression ignition engines. This study reports an experimental investigation into the effects of valve timings on HCCI combustion conditions. Using a single cylinder engine with state-of-the-art electromagnetic variable valve timing (EVVT) fully independent valves, a series of tests are conducted with varying negative valve overlap (NVO). The in-cylinder residual trapped by the NVO causes an advance in combustion timing, a shortening of burn duration as well as increase in load and increase in brake specific fuel consumption. Asymmetric valve timings are also investigated and show complex behavior with high sensitivity of combustion timing in certain operating ranges. Finally, these strategies are implemented as a set of feedback controllers including a proportional-integral (PI) controller and a feedforward with integral action controller. Both controllers have good tracking for step changes in combustion timing setpoint with the feedforward controller providing a rise time of just four cycles.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
In recent years a number of studies have demonstrated that boosted operation combined with external EGR is a path forward for expanding the high load limit of homogeneous charge compression ignition (HCCI) operation with the negative valve overlap (NVO) valve strategy. However, the effects of fuel composition with this strategy have not been fully explored. In this study boosted HCCI combustion is investigated in a single-cylinder research engine equipped with direct injection (DI) fueling, cooled external exhaust gas recirculation (EGR), laboratory pressurized intake air, and a fully-variable hydraulic valve actuation (HVA) valve train. Three fuels with significant compositional differences are investigated: regular grade gasoline (RON = 90.2), 30% ethanol-gasoline blend (E30, RON = 100.3), and 24% iso-butanol-gasoline blend (IB24, RON = 96.6). Results include engine loads from 350 to 800 kPa IMEPg for all fuels at three engine speeds 1600, 2000, and 2500 rpm. All operating conditions achieved thermal efficiency (gross indicated efficiency) between 38 and 47%, low NOX emissions (0.1 g/kWh), and high combustion efficiency (96.5%). Detailed sweeps of intake manifold pressure (atmospheric to 250 kPaa), EGR (0 25% EGR), and injection timing are conducted to identify fuel-specific effects. The major finding of this study is that while significant fuel compositional differences exist, in boosted HCCI operation only minor changes in operational conditions are required to achieve comparable operation for all fuels. In boosted HCCI operation all fuels were able to achieve matched load-speed operation, whereas in conventional SI operation the fuel-specific knock differences resulted in significant differences in the operable load-speed space. Although all fuels were operable in boosted HCCI, the respective air handling requirements are also discussed, including an analysis of the demanded turbocharger efficiency.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Abstract : The Homogeneous Charge Compression Ignition (HCCI) engine is a promising combustion concept for reducing NOx and particulate matter (PM) emissions and providing a high thermal efficiency in internal combustion engines. This concept though has limitations in the areas of combustion control and achieving stable combustion at high loads. For HCCI to be a viable option for on-road vehicles, further understanding of its combustion phenomenon and its control are essential. Thus, this thesis has a focus on both the experimental setup of an HCCI engine at Michigan Technological University (MTU) and also developing a physical numerical simulation model called the Sequential Model for Residual Affected HCCI (SMRH) to investigate performance of HCCI engines. The primary focus is on understanding the effects of intake and exhaust valve timings on HCCI combustion. For the experimental studies, this thesis provided the contributions for development of HCCI setup at MTU. In particular, this thesis made contributions in the areas of measurement of valve profiles, measurement of piston to valve contact clearance for procuring new pistons for further studies of high geometric compression ratio HCCI engines. It also consists of developing and testing a supercharging station and the setup of an electrical air heater to extend the HCCI operating region. The HCCI engine setup is based on a GM 2.0 L LHU Gen 1 engine which is a direct injected engine with variable valve timing (VVT) capabilities. For the simulation studies, a computationally efficient modeling platform has been developed and validated against experimental data from a single cylinder HCCI engine. In-cylinder pressure trace, combustion phasing (CA10, CA50, BD) and performance metrics IMEP, thermal efficiency, and CO emission are found to be in good agreement with experimental data for different operating conditions. Effects of phasing intake and exhaust valves are analyzed using SMRH. In addition, a novel index called Fuel Efficiency and Emissions (FEE) index is defined and is used to determine the optimal valve timings for engine operation through the use of FEE contour maps.
Author: Hsien-Hsin Liao Publisher: Stanford University ISBN: Category : Languages : en Pages : 201
Book Description
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: Alexander E. Schramm
Author: Alexander E. Schramm
Author: Keitaro Okuno
Author: Dennis G. Nitz
Author: John O. Waldman
Author: Tanet Aroonsrisopon
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Author: 
Author: Jacob Richard Zuehl
Author: 
Author: Hsien-Hsin Liao