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Author: Nathan Charles Anderson
Publisher:
ISBN:
Category :
Languages : en
Pages : 72
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Book Description
The implementation of homogenous charge compression ignition (HCCI) to gasoline engines is constrained by many factors. This work examines constrains imposed by nitric oxide (NOx) emission and by the need to maintain a minimum catalyst temperature on HCCI operation. Then the nature of the approach to high load limit was examined for three fuels with very different behavior. An engine simulation was used to examine constrains imposed by NOx emission and by catalyst temperature requirement. The valve timing in a HCCI engine using NegativeValve-Overlap (NVO) was varied in the simulation to control the operating point. The engine speed and intake pressure (turbocharged mode) were varied. The High Load Limit (HLL) was attained when the NOx emission reached the regulated level for a Partial-Zero-Emissions-Vehicle (PZEV). This occurred when the engine was running at the lowest speed and the highest intake pressure. Unreasonably large residual fraction was required to achieve the NOx limit unless a three-way catalyst is used. The engine behavior in the operating trajectory to the HLL was examined by using two Primary Reference fuels (PRF60 and PRF90) and a fuel blended from refinery feed stock. The latter fuel had Extremely Low Aromatic and Olefin content and is referred to as the ELAO fuel. For PRF60 (the knock prone fuel), the Maximum Pressure Rise Rate (MPRR) increased with increase in load (by reduction of residual). The HLL was attained when the MPRR reached a pre-determined level of 5MPa/ms. For PRF90 (the knock resistant fuel), however, the MPRR decreased with increase in load, and the HLL was constrained by ignition failure. For the ELAO fuel, the MPRR first increased and then decreased with increase in load. The HLL was thus constrained by ignition failure. Thus depending on the fuel properties, there could be very different engine behaviors in the approach to the HLL of HCCI operation.
Author: Nathan Charles Anderson
Publisher:
ISBN:
Category :
Languages : en
Pages : 72
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Book Description
The implementation of homogenous charge compression ignition (HCCI) to gasoline engines is constrained by many factors. This work examines constrains imposed by nitric oxide (NOx) emission and by the need to maintain a minimum catalyst temperature on HCCI operation. Then the nature of the approach to high load limit was examined for three fuels with very different behavior. An engine simulation was used to examine constrains imposed by NOx emission and by catalyst temperature requirement. The valve timing in a HCCI engine using NegativeValve-Overlap (NVO) was varied in the simulation to control the operating point. The engine speed and intake pressure (turbocharged mode) were varied. The High Load Limit (HLL) was attained when the NOx emission reached the regulated level for a Partial-Zero-Emissions-Vehicle (PZEV). This occurred when the engine was running at the lowest speed and the highest intake pressure. Unreasonably large residual fraction was required to achieve the NOx limit unless a three-way catalyst is used. The engine behavior in the operating trajectory to the HLL was examined by using two Primary Reference fuels (PRF60 and PRF90) and a fuel blended from refinery feed stock. The latter fuel had Extremely Low Aromatic and Olefin content and is referred to as the ELAO fuel. For PRF60 (the knock prone fuel), the Maximum Pressure Rise Rate (MPRR) increased with increase in load (by reduction of residual). The HLL was attained when the MPRR reached a pre-determined level of 5MPa/ms. For PRF90 (the knock resistant fuel), however, the MPRR decreased with increase in load, and the HLL was constrained by ignition failure. For the ELAO fuel, the MPRR first increased and then decreased with increase in load. The HLL was thus constrained by ignition failure. Thus depending on the fuel properties, there could be very different engine behaviors in the approach to the HLL of HCCI operation.
Author: Paul E. Yelvington
Publisher:
ISBN:
Category :
Languages : en
Pages : 261
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Book Description
The homogeneous-charge compression-ignition (HCCI) engine is a novel engine technology with the potential to substantially lower emissions from automotive sources. HCCI engines use lean-premixed combustion to achieve good fuel economy and low emissions of nitrogen-oxides and particulate matter. However, experimentally these engines have demonstrated a viable operating range that is too narrow for vehicular applications. Incomplete combustion or misfire can occur under fuel-lean conditions imposing a minimum load at which the engine can operate. At high loads, HCCI engines are often extremely loud and measured cylinder pressures show strong acoustic oscillations resembling those for a knocking sparkignited engine. The goal of this research was to understand the factors limiting the HCCI range of operability and propose ways of broadening that range. An engine simulation tool was developed to model the combustion process in the engine and predict HCCI knock and incomplete combustion. Predicting HCCI engine knock is particularly important because knock limits the maximum engine torque, and this limitation is a major obstacle to commercialization. A fundamentally-based criterion was developed and shown to give good predictions of the experimental knock limit. Our engine simulation tool was then used to explore the effect of various engine design parameters and operating conditions on the HCCI viable operating range. Performance maps, which show the response of the engine during a normal driving cycle, were constructed to compare these engine designs. The simulations showed that an acceptably broad operating range can be achieved by using a low compression ratio, low octane fuel, and moderate boost pressure. An explanation of why this choice of parameters gives a broad operating window is discussed. Our prediction of the HCCI knock limit is based on the autoignition theory of knock, which asserts that local overpressures in the engine are caused by extremely rapid chemical energy release. A competing theory asserts that knock is caused by the formation of detonation waves initiated at autoignition centers ('hot-spots') in the engine. No conclusive experimental evidence exists for the detonation theory, but many numerical simulations in the literature show that detonation formation is possible; however, some of the assumptions made in these simulations warrant re-examination. In particular, the effect of curvature on small (quasispherical) hot-spots has often been overlooked. We first examined the well-studied case of gasoline spark-ignited engine knock and observed that the size of the hot-spot needed to initiate a detonation is larger than the end-gas region where knock occurs. Subsequent studies of HCCI engine knock predicted that detonations would not form regardless of the hot-spot size because of the low energy content of fuel-lean mixtures typically used in these engines. Our predictions of the HCCI viable operating range were shown to be quite sensitive to details of the ignition chemistry. Therefore, an attempt was made to build an improved chemistry model for HCCI combustion using automatic mechanism-generation software developed in our research group. Extensions to the software were made to allow chemistry model construction for engine conditions. Model predictions for n-heptane/air combustion were compared to literature data from a jet-stirred reactor and rapid-compression machine. We conclude that automatic mechanism generation gives fair predictions without the tuning of rate parameters or other efforts to improve agreement. However, some tuning of the automatically-generated chemistry models is necessary to give the accurate predictions of HCCI combustion needed for our design calculations.
Author: Hua Zhao
Publisher: CRC Press
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 562
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Book Description
Homogeneous charge compression ignition (HCCI)/controlled auto-ignition (CAI) has emerged as one of the most promising engine technologies with the potential to combine fuel efficiency and improved emissions performance, offering reduced nitrous oxides and particulate matter alongside efficiency comparable with modern diesel engines. Despite the considerable advantages, its operational range is rather limited and controlling the combustion (timing of ignition and rate of energy release) is still an area of on-going research. Commercial applications are, however, close to reality. HCCI a.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
While the potential emissions and efficiency benefits of homogeneous charge compression ignition (HCCI) combustion are well known, realizing the potentials on a production intent engine presents numerous challenges. In this study we focus on characterizing the authority of the available engine controls as the high load limit of HCCI combustion is approached. The experimental work is performed on a boosted single-cylinder research engine equipped with direct injection (DI) fueling, cooled external exhaust gas recirculation (EGR), and a hydraulic valve actuation (HVA) valve train to enable the negative valve overlap (NVO) breathing strategy. Valve lift and duration are held constant while phasing is varied in an effort to make the results as relevant as possible to production intent cam-based variable valve actuation (VVA) systems on multi-cylinder engines. Results presented include engine loads from 350 to 650 kPa IMEPnet and manifold pressure from 98 to 190 kPaa at 2000 rpm. It is found that in order to increase engine load to 650 kPa IMEPnet, it is necessary to increase manifold pressure and external EGR while reducing the NVO duration. Both NVO duration and fuel injection timing are effective means of controlling combustion phasing, with NVO duration being a coarse control and fuel injection timing being a fine control. NOX emissions are low throughout the study, with emissions below 0.1 g/kW-h at all boosted HCCI conditions, while good combustion efficiency is maintained (>96.5%). Net indicated thermal efficiency increases with load up to 600 kPa IMEPnet, where a peak efficiency of 41% is achieved. Results of independent parametric investigations are presented on the effect of external EGR, intake effect of manifold pressure, and the effect of NVO duration. It is found that increasing EGR at a constant manifold pressure and increasing manifold pressure at a constant EGR rate both have the effect of retarding combustion phasing. It is also found that combustion phasing becomes increasingly sensitive to NVO duration as engine load increases. Finally, comparisons are made between three commonly used noise metrics (AVL noise meter, ringing intensity (RI), and maximum pressure rise rate (MPRR)). It is found that compared to the AVL noise meter, RI significantly underestimates combustion noise under boosted conditions.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 20
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Book Description
Author: H Zhao
Publisher: Elsevier
ISBN: 184569354X
Category : Technology & Engineering
Languages : en
Pages : 557
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Book Description
Homogeneous charge compression ignition (HCCI)/controlled auto-ignition (CAI) has emerged as one of the most promising engine technologies with the potential to combine fuel efficiency and improved emissions performance, offering reduced nitrous oxides and particulate matter alongside efficiency comparable with modern diesel engines. Despite the considerable advantages, its operational range is rather limited and controlling the combustion (timing of ignition and rate of energy release) is still an area of on-going research. Commercial applications are, however, close to reality.HCCI and CAI engines for the automotive industry presents the state-of-the-art in research and development on an international basis, as a one-stop reference work. The background to the development of HCCI / CAI engine technology is described. Basic principles, the technologies and their potential applications, strengths and weaknesses, as well as likely future trends and sources of further information are reviewed in the areas of gasoline HCCI / CAI engines; diesel HCCI engines; HCCI / CAI engines with alternative fuels; and advanced modelling and experimental techniques. The book provides an invaluable source of information for scientific researchers, R&D engineers and managers in the automotive engineering industry worldwide. - Presents the state-of-the-art in research and development on an international basis - An invaluable source of information for scientific researchers, R&D engineers and managers in the automotive engineering industry worldwide - Looks at one of the most promising engine technologies around
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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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: Kushal Narayanaswamy
Publisher:
ISBN:
Category :
Languages : en
Pages : 226
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Author: Daniel Dahl
Publisher:
ISBN: 9789173856867
Category :
Languages : en
Pages : 183
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Book Description
Author: Joel Michael Cowgill
Publisher:
ISBN:
Category : Internal combustion engines
Languages : en
Pages : 338
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Book Description
Abstract: In order to meet future emissions requirements for internal combustion engines, continuing advances in emission reduction techniques are imperative. A method for in-cylinder emissions reduction currently being investigated quite extensively is Homogeneous Charge Compression Ignition (HCCI). An engine operating in pure HCCI combustion is capable of reducing NOx and PM emissions to near zero levels. However, HCCI engines are typically limited to low and mid-load operation due to high cylinder pressure-rise-rates associated with compression ignition of a homogeneous charge. One method of extending this operating range, investigated in this work, is the combination of HCCI combustion with standard CIDI combustion in a mixed-mode operating scheme. This method combines the emissions benefits of HCCI combustion with the high efficiency operation of standard Diesel combustion. Steady-state engine operating conditions are explored in pure HCCI and HCCI/DI mixed-mode operation and compared to baseline operating conditions of standard CIDI in a production 2.5L common rail Diesel engine. In this work, homogeneous mixture preparation is performed utilizing an external atomization device. In preliminary characterization, the effects of HCCI ratio, EGR ratio and DI timing are explored and the advantages of mixed-mode operation is verified over that of standard CIDI Diesel combustion. Following definition of the most important combustion control parameters, a comprehensive sensitivity analysis of EGR ratio, DI timing, engine speed and engine load is also conducted in mixed-mode operation with a focus on the effects of engine out emissions and combustion characteristics. Additionally, the limits of HCCI operation in this particular engine are also explored in order to define a baseline location for the transition to mixed-mode operation. In order to truly ascertain the benefits of mixed-mode combustion, results of mixed-mode operation are contrasted against manufacturer's engine maps for NOx and PM emissions as well as fuel consumption. The results of rough optimization illustrate that significant reduction in NOx emissions are possible with reasonable PM emissions easily eliminated with a current generation DPF. Fuel consumption is also found to be significantly reduced in most mixed-mode cases where up to 15 percent reductions are possible in the operating range considered. This fuel consumption decrease is also found to extend to pure HCCI operation and close to 10 percent reductions are discovered between operating speeds of 1500 and 2500 RPM at slightly more than 2 bar BMEP engine load. To set the stage for further research, basic transient operation is also investigated. With a firm grasp and understanding of steady-state operating conditions, control of the transition between pure HCCI, mixed-mode and pure CIDI combustion schemes can be explored. The basic structure of this control format includes pure HCCI operation at low-loads, mixed-mode operation in mid-loads and standard CIDI operation at high-loads. In this work, HCCI operation is found to be relatively insensitive to engine speed; however, increases in engine speed may affect the load threshold conditions at which these transitions occur.
