Modeling the Effects of Variable Intake Valve Timing on Diesel HCCI Combustion at Varying Load, Speed, and Boost Pressures

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
C. L. Genzale ◽  
S.-C. Kong ◽  
R. D. Reitz
Keyword(s):  
Operating Conditions ◽  
Effective Control ◽  
Intake Valve ◽  
Valve Timing ◽  
Detailed Chemical Kinetics ◽  
Hcci Combustion ◽  
Wide Range ◽  
Particulate Matter Emissions ◽  
Charge Mixture ◽  
Ignition And Combustion

Homogeneous charge compression ignition (HCCI) operated engines have the potential to provide the efficiency of a typical diesel engine, with very low NOx and particulate matter emissions. However, one of the main challenges with this type of operation in diesel engines is that it can be difficult to control the combustion phasing, especially at high loads. In diesel HCCI engines, the premixed fuel-air charge tends to ignite well before top dead center, especially as load is increased, and a method of delaying the ignition is necessary. The development of variable valve timing (VVT) technology may offer an important advantage in the ability to control diesel HCCI combustion. VVT technology can allow for late intake valve closure (IVC) times, effectively changing the compression ratio of the engine. This can decrease compression temperatures and delay ignition, thus allowing the possibility to employ HCCI operation at higher loads. Furthermore, fully flexible valve trains may offer the potential for dynamic combustion phasing control over a wide range of operating conditions. A multidimensional computational fluid dynamics model is used to evaluate combustion event phasing as both IVC times and operating conditions are varied. The use of detailed chemical kinetics, based on a reduced n-heptane mechanism, provides ignition and combustion predictions and includes low-temperature chemistry. The use of IVC delay is demonstrated to offer effective control of diesel HCCI combustion phasing over varying loads, engine speeds, and boost pressures. Additionally, as fueling levels are increased, charge mixture properties are observed to have a significant effect on combustion phasing. While increased fueling rates are generally seen to advance combustion phasing, the reduction of specific heat ratio in higher equivalence ratio mixtures can also cause noticeably slower temperature rise rates, affecting ignition timing and combustion phasing. Variable intake valve timing may offer a promising and flexible control mechanism for the phasing of diesel HCCI combustion. Over a large range of boost pressures, loads, and engine speeds, the use of delayed IVC is shown to sufficiently delay combustion in order to obtain optimal combustion phasing and increased work output, thus pointing towards the possibility of expanding the current HCCI operating range into higher load points.

Modeling the Effects of Variable Intake Valve Timing on Diesel HCCI Combustion at Varying Load, Speed and Boost Pressures

2005 ◽  
Author(s):  
Caroline L. Dougan ◽  
Song-Charng Kong ◽  
Rolf D. Reitz
Keyword(s):  
Operating Conditions ◽  
Boost Pressure ◽  
Combustion Control ◽  
Intake Valve ◽  
Valve Timing ◽  
Detailed Chemical Kinetics ◽  
Available N ◽  
Hcci Combustion ◽  
Auto Ignition ◽  
Variable Valve

It is well known that homogeneous charge compression ignition (HCCI) operated engines have the potential to provide the efficiency of a typical diesel engine, but with very low NOx and Particulate Matter (PM) emissions. One of the main challenges with this type of engine, however, is that it can be difficult to control the combustion event, especially at high loads. The development of Variable Valve Timing (VVT) technology may offer an important advantage in the ability to control HCCI combustion. This work investigates the potential of using late intake valve closure times to delay auto-ignition and to expand the HCCI operation range through proper combustion control. A multi-dimensional KIVA/Chemkin model is used in conjunction with detailed chemical kinetics, based on an available n-heptane mechanism. The model is used to evaluate the effectiveness of late intake valve times as load, speed, and boost pressure conditions are varied. Furthermore, a larger understanding of diesel HCCI combustion is sought by investigating the major parameters affecting combustion control under these various operating conditions.

Physically-Based Volumetric Efficiency Model for Diesel Engines Utilizing Variable Intake Valve Actuation

2011 ◽  
Author(s):  
Lyle Kocher ◽  
Ed Koeberlein ◽  
D. G. Van Alstine ◽  
Karla Stricker ◽  
Greg Shaver
Keyword(s):  
Diesel Engine ◽  
Fuel Injection ◽  
Operating Conditions ◽  
Volumetric Efficiency ◽  
Intake Valve ◽  
Valve Timing ◽  
Tuning Parameters ◽  
Wide Range ◽  
Physically Based ◽  
Valve Actuation

Advanced diesel engine architectures employing flexible valve trains enable emissions reductions and fuel economy improvements. Flexibility in the valve train allows engine designers to optimize the gas exchange process in a manner similar to how common rail fuel injection systems enable optimization of the fuel injection process. Modulating valve timings directly impacts the volumetric efficiency of the engine. In fact, the control authority of valve timing modulation over volumetric efficiency is three times larger than that due to any other engine actuator. Traditional empirical or regression-based models for volumetric efficiency, while suitable for conventional valve trains, are therefore challenged by flexible valve trains. The added complexity and additional empirical data needed for wide valve timing ranges limit the usefulness of these methods. A physically-based volumetric efficiency model was developed to address these challenges. The model captures the major physical processes occurring over the intake stroke, and is applicable to both conventional and flexible valve trains. The model inputs include temperature and pressure in the intake and exhaust manifolds, intake and exhaust valve timings, bore, stoke, connecting rod length, engine speed and effective compression ratio, ECR. The model is physically-based, requires no regression tuning parameters, is generalizable to other engine platforms, and has been experimentally validated using an advanced multi-cylinder diesel engine equipped with a flexible variable intake valve actuation system. Experimental data was collected over a wide range of the operating space of the engine and augmented with air handling actuator and intake valve timing sweeps to maximize the range of conditions used to thoroughly experimentally validate the model for a total of 217 total operating conditions. The physical model developed differs from previous physical modeling work through the novel application of ECR, incorporation of no tuning parameters and extensive validation on unique engine test bed with flexible intake valve actuation.

scholarly journals Assessment of the Magnetic Hysteretic Behaviour of MR Dampers through Sensorless Measurements

2018 ◽  
Vol 2018 ◽  
pp. 1-21 ◽  
Author(s):  
Janusz Gołdasz ◽  
Bogdan Sapinski ◽  
Łukasz Jastrzębski
Keyword(s):  
Magnetic Hysteresis ◽  
Operating Conditions ◽  
Effective Control ◽  
Flow Mode ◽  
Shear Mode ◽  
Hysteretic Behaviour ◽  
Mr Dampers ◽  
Smart Fluids ◽  
Wide Range ◽  
And Control

Magnetorheological (MR) dampers are well-known devices based on smart fluids. The dampers exhibit nonlinear hysteretic behaviour which affects their performance in control systems. Hence, an effective control scheme must include a hysteresis compensator. The source of hysteresis in MR dampers is twofold. First, it is due to the compressibility and inertia of the fluid. Second, magnetic hysteresis is the inherent property of ferromagnetic materials that form the control circuit of the valve including MR fluid. While the former was studied extensively over the past years using various phenomenological models, the latter has attracted less attention. In this paper, we analyze the magnetic hysteretic behaviour of three different MR dampers by investigating their current-flux relationships. Two dampers operate in flow mode, whereas the third one is a shear-mode device (brake). The approach is demonstrated using a sensorless magnetic flux estimation technique. We reveal the response of the dampers when subjected to sinusoidal inputs across a wide range of operating conditions and excitation inputs. Our observations of the flux data showed that the hysteresis is influenced by both amplitude and the frequency of the excitation input. The procedure allows to analyze the magnetic hysteresis independently of other sources of hysteresis in MR dampers; on this basis, more effective damper models and control algorithms can be developed in the future.

Controlling Backfire Using Changes of the Valve Overlap Period for a Hydrogen-Fueled Engine Using an External Mixture

2007 ◽  
Author(s):  
T. C. Huynh ◽  
J. K. Kang ◽  
K. C. Noh ◽  
Jong T. Lee ◽  
J. A. Caton
Keyword(s):  
High Efficiency ◽  
Engine Performance ◽  
Continuous Variable ◽  
Operating Conditions ◽  
Variable Valve Timing ◽  
Valve Timing ◽  
Wide Range ◽  
Timing System ◽  
Variable Valve ◽  
Valve Overlap

The development of a hydrogen-fueled engine using an external mixture (e.g., using port or manifold fuel injection) with high efficiency and high power is dependent on the control of backfire. This work has developed a method to control backfire by reducing the valve overlap period while maintaining or improving engine performance. For this goal, a single-cylinder hydrogen-fueled research engine with a mechanical continuous variable valve timing system was developed. This facility provides a wide range of valve overlap periods that can be continuously and independently varied during firing operation. By using this research engine, the behavior of backfire occurrence and engine performance are determined as functions of the valve overlap period for fuel-air equivalence ratios between 0.3 and 1.2. The results showed that the developed hydrogen-fueled research engine with the mechanical continuous variable valve timing system has similar performance to a conventional engine with fixed valve timings, and is especially effective in controlling the valve overlap period. Backfire occurrence is reduced with a decrease of the valve overlap period, and is also significantly decreased even under operating conditions with the same volumetric efficiency. These results demonstrate that decreasing the valve overlap period may be one of the methods for controlling backfire in a hydrogen-fueled engine while maintaining or improving performance.

Controlling Backfire for a Hydrogen-Fueled Engine Using External Mixture Injection

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
T. C. Huynh ◽  
J. K. Kang ◽  
K. C. Noh ◽  
Jong T. Lee ◽  
J. A. Caton
Keyword(s):  
High Efficiency ◽  
Engine Performance ◽  
Continuous Variable ◽  
Operating Conditions ◽  
Variable Valve Timing ◽  
Valve Timing ◽  
Wide Range ◽  
Timing System ◽  
Variable Valve ◽  
Valve Overlap

The development of a hydrogen-fueled engine using external mixture injection (e.g., using port or manifold fuel injection) with high efficiency and high power is dependent on the control of backfire. This work has developed a method to control backfire by reducing the valve overlap period while maintaining or improving engine performance. For this goal, a single-cylinder hydrogen-fueled research engine with a mechanical continuous variable valve timing system was developed. This facility provides a wide range of valve overlap periods that can be continuously and independently varied during firing operation. By using this research engine, the behavior of backfire occurrence and engine performance are determined as functions of the valve overlap period for fuel-air equivalence ratios between 0.3 and 1.2. The results showed that the developed hydrogen-fueled research engine with the mechanical continuous variable valve timing system has similar performance to a conventional engine with fixed valve timings, and is especially effective in controlling the valve overlap period. Backfire occurrence is reduced with a decrease in the valve overlap period, and is also significantly decreased even under operating conditions with the same volumetric efficiency. These results demonstrate that decreasing the valve overlap period may be one of the methods for controlling backfire in a hydrogen-fueled engine while maintaining or improving performance.

Application of Variable Valve Actuation Strategies and Direct Gasoline Injection Schemes to Reduce Combustion Harshness and Emissions of Boosted HCCI Engine

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Jacek Hunicz ◽  
Maciej Mikulski
Keyword(s):  
Pressure Rise ◽  
Operating Conditions ◽  
Exhaust Valve ◽  
Boost Pressure ◽  
Pressure Reduction ◽  
Intake Valve ◽  
Valve Timing ◽  
Hcci Engine ◽  
Auto Ignition ◽  
The Impact

The present study investigates various measures to reduce pressure rise rates (PRRs) in a residual-affected homogeneous charge compression ignition (HCCI) engine. At the same time, the impact of those measures on efficiency and emissions is assessed. Experimental research was performed on a single cylinder engine equipped with a fully flexible valve train mechanism and direct gasoline injection. The HCCI combustion mode with exhaust gas trapping was realized using negative valve overlap (NVO) and fuel reforming, achieved via the injection of a portion of fuel during exhaust recompression. Three measures are investigated for the PRR control under the same reference operating conditions, namely: (i) variable intake and exhaust valve timing, (ii) boost pressure adjustment, and (iii) split fuel injection to control the amount of fuel injected for reforming. Variable exhaust valve timing enabled control of the amount of trapped residuals, and thus of the compression temperature. The reduction in the amount of trapped residuals, at elevated engine load, delays auto-ignition, which results in a simultaneous reduction of pressure rise rates and nitrogen oxides emissions. The effects of intake valve timing are much more complex because they include the variability in the amount of intake air, the thermodynamic compression ratio, as well as the in-cylinder fluid flow. It was found, however, that both early and late intake valve openings (IVOs) delay auto-ignition and prolong combustion. Additionally, the reduction of the amount of fuel injected during exhaust recompression further delays combustion and reduces combustion rates. Intake pressure reduction has by far the largest effect on peak pressure reduction yet is connected with excessive NOX emissions. The research successfully identifies air-path and injection techniques, which allow for the control of combustion rates and emissions under elevated load regime.

scholarly journals The NOx and N2O Emission Characteristics of an HCCI Engine Operated With n-Heptane

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Hailin Li ◽  
W. Stuart Neill ◽  
Hongsheng Guo ◽  
Wally Chippior
Keyword(s):  
N2o Emission ◽  
Combustion Efficiency ◽  
Operating Conditions ◽  
N2o Emissions ◽  
Emission Characteristics ◽  
Nox Emissions ◽  
Oxides Of Nitrogen ◽  
Incomplete Combustion ◽  
Hcci Combustion ◽  
Wide Range

This paper presents the oxides of nitrogen (NOx) and nitrous oxide (N2O) emission characteristics of a Cooperative Fuel Research (CFR) engine modified to operate in homogeneous charge compression ignition (HCCI) combustion mode. N-heptane was used as the fuel in this research. Several parameters were varied, including intake air temperature and pressure, air/fuel ratio (AFR), compression ratio (CR), and exhaust gas recirculation (EGR) rate, to alter the HCCI combustion phasing from an overly advanced condition where knocking occurred to an overly retarded condition where incomplete combustion occurred with excessive emissions of unburned hydrocarbons (UHC) and carbon monoxide (CO). NOx emissions below 5 ppm were obtained over a fairly wide range of operating conditions, except when knocking or incomplete combustion occurred. The NOx emissions were relatively constant when the combustion phasing was within the acceptable range. NOx emissions increased substantially when the HCCI combustion phasing was retarded beyond the optimal phasing even though lower combustion temperatures were expected. The increased N2O and UHC emissions observed with retarded combustion phasing may contribute to this unexpected increase in NOx emissions. N2O emissions were generally less than 0.5 ppm; however, they increased substantially with excessively retarded and incomplete combustion. The highest measured N2O emissions were 1.7 ppm, which occurred when the combustion efficiency was approximately 70%.

Thermal Charge Conditioning for Optimal HCCI Engine Operation

2002 ◽  
Vol 124 (1) ◽  
pp. 67-75 ◽  
Author(s):  
Joel Martinez-Frias ◽  
Salvador M. Aceves ◽  
Daniel Flowers ◽  
J. Ray Smith ◽  
Robert Dibble
Keyword(s):  
High Efficiency ◽  
Thermal Control ◽  
Operating Conditions ◽  
Cylinder Pressure ◽  
Detailed Chemical Kinetics ◽  
Engine Operation ◽  
Hcci Engine ◽  
Peak Cylinder Pressure ◽  
Wide Range ◽  
Gas Recirculation

This work investigates a purely thermal control system for HCCI engines, where thermal energy from exhaust gas recirculation (EGR) and compression work in the supercharger are either recycled or rejected as needed. HCCI engine operation is analyzed with a detailed chemical kinetics code, HCT (Hydrodynamics, Chemistry and Transport), which has been extensively modified for application to engines. HCT is linked to an optimizer that determines the operating conditions that result in maximum brake thermal efficiency, while meeting the restrictions of low NOx and peak cylinder pressure. The results show the values of the operating conditions that yield optimum efficiency as a function of torque for a constant engine speed (1800 rpm). For zero torque (idle), the optimizer determines operating conditions that result in minimum fuel consumption. The optimizer is also used for determining the maximum torque that can be obtained within the operating restrictions of NOx and peak cylinder pressure. The results show that a thermally controlled HCCI engine can successfully operate over a wide range of conditions at high efficiency and low emissions.

Modeling Direct-Injection Gasoline HCCI Combustion Using Detailed Chemistry and CFD

2001 ◽  
Author(s):  
Song-Charng Kong ◽  
Rolf D. Reitz
Keyword(s):  
Turbulent Mixing ◽  
Direct Injection ◽  
Combustion Process ◽  
Reaction Rates ◽  
Injection Timing ◽  
Detailed Chemical Kinetics ◽  
Detailed Chemistry ◽  
Hcci Combustion ◽  
Wide Range ◽  
Hcci Engines

Abstract Detailed chemical kinetics was implemented into an engine CFD code to study the combustion process in Homogeneous Charge Compression Ignition (HCCI) engines. The CHEMKIN code was implemented into KIVA-3V such that the chemistry and flow solutions were coupled. Effects of turbulent mixing on the reaction rates were also considered. The model was validated using experimental data from a direct-injection Caterpillar engine operated in the HCCI mode using gasoline. The results show that good levels of agreement were obtained using the present KIVA/CHEMKIN model for a wide range of engine conditions including various injection timings, engine speeds, and loads. It was found that the effects of turbulent mixing on the reaction rates needed to be considered to correctly simulate the combustion phasing. It was also found that the presence of residual radicals could enhance the mixture reactivity and hence shorten the ignition delay time. The NOx emissions were found to increase as the injection timing was retarded, in agreement with experimental results.

Application of Variable Valve Actuation Strategies and Direct Gasoline Injection Schemes to Reduce Combustion Harshness and Emissions of Boosted HCCI Engine

2018 ◽  
Author(s):  
Jacek Hunicz ◽  
Maciej Mikulski
Keyword(s):  
Pressure Rise ◽  
Operating Conditions ◽  
Exhaust Valve ◽  
Boost Pressure ◽  
Pressure Reduction ◽  
Intake Valve ◽  
Valve Timing ◽  
Hcci Engine ◽  
Auto Ignition ◽  
The Impact

One of the pending issues regarding Homogeneous Charge Compression Ignition (HCCI) engines is high load operation limit constrained by excessive pressure rise rates (PRRs). The present study investigates various measures to reduce combustion harness in a residual-affected HCCI engine. At the same time, the impact of those measures on efficiency and emissions is assessed. Experimental research was performed on a single cylinder engine equipped with a fully-flexible valvetrain mechanism and direct gasoline injection. The HCCI combustion mode with exhaust gas trapping was realized using negative valve overlap and fuel reforming, achieved via the injection of a portion of fuel during exhaust re-compression. Three measures are investigated for the PRR control under the same reference operating conditions, namely: (i) variable intake and exhaust valve timing, (ii) boost pressure adjustment and (iii) split fuel injection to control the amount of fuel injected for reforming. Variable exhaust valve timing enabled control of the amount of trapped residuals, and thus of the compression temperature. The reduction in the amount of trapped residuals, at elevated engine load, delays auto-ignition, which results in a simultaneous reduction of pressure rise rates and nitrogen oxides emissions. The effects of intake valve timing are much more complex, because they include the variability in the amount of intake air, the thermodynamic compression ratio as well as the in-cylinder fluid flow. It was found, however, that both early and late intake valve openings delay auto-ignition and prolong combustion. Additionally, the reduction of the amount of fuel injected during exhaust re-compression further delays combustion and reduces combustion rates. Intake pressure reduction has by far the largest effect on peak pressure reduction yet is connected with excessive NOx emissions. The research successfully identifies air-path and injection techniques, which allow for the control of combustion rates and emissions under elevated load regime, thus shorting the gap towards the real-world application of HCCI concepts.

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