Quantifying Cyclic Variability in a Multicylinder HCCI Engine With High Residuals

2012 ◽  
Vol 134 (11) ◽  
Author(s):  
Erik Hellström ◽  
Jacob Larimore ◽  
Anna Stefanopoulou ◽  
Jeff Sterniak ◽  
Li Jiang
Keyword(s):  
Single Cylinder ◽  
Cyclic Variability ◽  
Cycle Basis ◽  
Hcci Combustion ◽  
Single Cylinder Engine ◽  
Operating Limits ◽  
Unburned Fuel ◽  
The Individual ◽  
Negative Valve Overlap ◽  
Valve Overlap

Cyclic variability (CV) in lean homogeneous charge compression ignition (HCCI) combustion at the limits of operation is a known phenomenon, and this work aims at investigating the dominant effects for the cycle evolution at these conditions in a multicylinder engine. Experiments are performed in a four-cylinder engine at the operating limits at late phasing of lean HCCI operation with negative valve overlap (nvo). A combustion analysis method that estimates the unburned fuel mass on a per-cycle basis is applied on both main combustion and the nvo period revealing and quantifying the dominant effects for the cycle evolution at high CV. The interpretation of the results and comparisons with data from a single-cylinder engine indicate that, at high CV, the evolution of combustion phasing is dominated by low-order deterministic couplings similar to the single-cylinder behavior. Variations, such as air flow and wall temperature, between cylinders strongly influence the level of CV but the evolution of the combustion phasing is governed by the interactions between engine cycles of the individual cylinders.

Quantifying Cyclic Variability in a Multi-Cylinder HCCI Engine With High Residuals

2012 ◽  
Author(s):  
Erik Hellström ◽  
Jacob Larimore ◽  
Anna Stefanopoulou ◽  
Jeff Sterniak ◽  
Li Jiang
Keyword(s):  
Single Cylinder ◽  
Cyclic Variability ◽  
Cycle Basis ◽  
Hcci Combustion ◽  
Single Cylinder Engine ◽  
Operating Limits ◽  
Unburned Fuel ◽  
The Individual ◽  
Negative Valve Overlap ◽  
Valve Overlap

Cyclic variability (CV) in lean HCCI combustion at the limits of operation is a known phenomenon, and this work aims at investigating the dominant effects for the cycle evolution at these conditions in a multi-cylinder engine. Experiments are performed in a four-cylinder engine at the operating limits at late phasing of lean HCCI operation with negative valve overlap (nvo). A combustion analysis method that estimates the unburned fuel mass on a per-cycle basis is applied on both main combustion and the nvo period revealing and quantifying the dominant effects for the cycle evolution at high CV. The interpretation of the results and comparisons with data from a single-cylinder engine indicate that, at high CV, the evolution of combustion phasing is dominated by low-order deterministic couplings similar to the single-cylinder behavior. Variations, such as in air flow and wall temperature, between cylinders strongly influence the level of CV but the evolution of the combustion phasing is governed by the interactions between engine cycles of the individual cylinders.

Understanding the Dynamic Evolution of Cyclic Variability at the Operating Limits of HCCI Engines with Negative Valve Overlap

2012 ◽  
Vol 5 (3) ◽  
pp. 995-1008 ◽  
Author(s):  
Erik Hellström ◽  
Anna Stefanopoulou ◽  
Jiri Vavra ◽  
Aristotelis Babajimopoulos ◽  
Dennis N. Assanis ◽  
...  
Keyword(s):  
Dynamic Evolution ◽  
Cyclic Variability ◽  
Hcci Engines ◽  
Operating Limits ◽  
Negative Valve Overlap ◽  
Valve Overlap

Effect of Fuel Injection Timing During Negative Valve Overlap Period on a GDI-HCCI Engine

2018 ◽  
Author(s):  
Sok Ratnak ◽  
Jin Kusaka ◽  
Yasuhiro Daisho ◽  
Kei Yoshimura ◽  
Kenjiro Nakama
Keyword(s):  
Fuel Injection ◽  
Direct Injection ◽  
Single Pulse ◽  
Injection Timing ◽  
Pulse Injection ◽  
Hcci Combustion ◽  
Fuel Injection Timing ◽  
Intake Stroke ◽  
Negative Valve Overlap ◽  
Valve Overlap

Gasoline Direct Injection Homogeneous Charge Compression (GDI-HCCI) combustion is achieved by closing early the exhaust valves for trapping hot residual gases combined with direct fuel injection. The combustion is chemically controlled by multi-point auto-ignition which its main combustion phase can be controlled by direct injection timing of fuel. This work investigates the effect of single pulse injection timing on a supercharged GDI-HCCI combustion engine by using a four-stroke single cylinder engine with a side-mounted direct fuel injector. Injection of primary reference fuel PRF90 under the near-stoichiometric-boosted condition is studied. The fuel is injected during negative valve overlap (NVO) or recompression period for fuel reformation under low oxygen concentration and the injection is retarded to intake stroke for the homogeneous mixture. It is found that the early fuel injection in NVO period advances the combustion phasing compared with the retarded injection in the intake stroke. Noticeable slower combustion rate from intake stroke fuel injection is obtained compared with the NVO injection due to charge cooling effect. Zero-dimensional combustion simulations with multiple chemical reaction mechanisms are simulated to provide chemical understanding from the effect of fuel injection timing on intermediate species generations. The species such as C2H4, C3H6, CH4, and H2 are found to be formed during the NVO injection period from the calculations. The effects of single pulse injection timings on combustion characteristics such pressure rise rate, combustion stability, and emissions are also discussed in this study.

Trapped Unburned Fuel Estimation and Robustness Analysis for a Turbocharged Diesel Engine With Negative Valve Overlap Strategy

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Song Chen ◽  
Fengjun Yan
Keyword(s):  
Theoretical Analysis ◽  
Internal Combustion Engines ◽  
Combustion Process ◽  
Robustness Analysis ◽  
Linear Matrix ◽  
Fuel Mass ◽  
Residual Gas ◽  
Unburned Fuel ◽  
Negative Valve Overlap ◽  
Valve Overlap

Turbocharger and negative valve overlap (NVO) strategy are widely used among advanced combustion modes for internal combustion engines. In order to achieve well emission performance, the NVO can be as large as 100 crank angle (CA) degrees, such that the residual gas fraction can be up to 40%. With such amount of residual gas in the cylinder, the trapped unburned fuel is not trivial. It has a significant impact on the combustion process. However, the trapped unburned fuel mass is hard to be measured directly. In this paper, a novel method based on the signals of oxygen fraction is proposed to estimate it. By analyzing the combustion process, dynamic equations for the intake/exhaust manifolds and in-cylinder oxygen fractions, as well as actual fuel mass in the cylinder are constructed. A smooth variable structure filter (SVSF) was designed to estimate oxygen fractions and further the trapped unburned fuel. As a comparison, Kalman filter (KF) and linear matrix inequality (LMI) based linear parameter-varying (LPV) filter were also applied. Robustness properties of the three observers are analyzed based on the theory of input-to-state (ISS) stability. The proposed models and methods and theoretical analysis are validated and compared through a set of simulations in high-fidelity GT-Power environment. The simulation results match well with theoretical analysis that the SVSF has good properties of strong robustness (with a root mean square error (RMSE) of 0.24, comparing with 0.4 of LPV filter and 0.49 of KF, for the unburned fuel estimation).

An integrated model for negative valve overlap early injection HCCI combustion

2014 ◽  
Vol 87 (4) ◽  
pp. 341-353 ◽  
Author(s):  
Yong Gui ◽  
Kangyao Deng ◽  
Min Xu ◽  
Lei Shi ◽  
Youcheng Sun
Keyword(s):  
Integrated Model ◽  
Hcci Combustion ◽  
Negative Valve Overlap ◽  
Valve Overlap ◽  
Early Injection

Internal Residual vs. Elevated Intake Temperature: How the Method of Charge Preheating Affects the Phasing Limitations of HCCI Combustion

2012 ◽  
Author(s):  
Laura Manofsky Olesky ◽  
Jiri Vavra ◽  
Dennis Assanis ◽  
Aristotelis Babajimopoulos
Keyword(s):  
Constant Load ◽  
Combustion Stability ◽  
Residual Fraction ◽  
Compression Ignition ◽  
Hcci Combustion ◽  
Final Study ◽  
Temperature Constant ◽  
Negative Valve Overlap ◽  
Burn Rate ◽  
Valve Overlap

Homogeneous charge compression ignition (HCCI) has the potential to reduce both fuel consumption and NOx emissons compared to normal spark-ignited (SI) combustion. For a relatively low compression ratio engine, high unburned temperatures are needed to initiate HCCI combustion, which is achieved with large amounts of internal residual or by heating the intake charge. The amount of residual in the combustion chamber is controlled by a recompression valve strategy, which relies on negative valve overlap (NVO) to trap residual gases in the cylinder. A single-cylinder research engine with fully-flexible valve actuation is used to explore the limits of HCCI combustion phasing at a constant load of ∼3 bar IMEPg. This is done by performing two individual sweeps of a) internal residual fraction (via NVO) and b) intake air temperature to control combustion phasing. It is found that increasing both variables advances the phasing of HCCI combustion, which leads to increased NOx emissions and a higher ringing intensity. On the other hand, a reduction in these variables leads to greater emissions of CO and HC, as well as a decrease in combustion stability. A direct comparison of the two sweeps suggests that the points with elevated intake temperatures are more prone to ringing as combustion is advanced and less prone to instability and misfire as combustion is retarded. This behavior can be explained by compositional differences (air vs. EGR dilution) which lead to variations in burn rate and peak temperature. As a final study, two additional NVO sweeps are performed while holding intake temperature constant at 30°C and 90°C. Again, it is seen that at higher intake temperatures, combustion is more susceptible to ringing at advanced timings and more resistant to instability/misfire at retarded timings.

Effects of a Low Octane Gasoline Blended Fuel on Negative Valve Overlap Enabled HCCI Load Limit, Combustion Phasing and Burn Duration

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Luke M. Hagen ◽  
Laura Manofsky Olesky ◽  
Stanislav V. Bohac ◽  
George Lavoie ◽  
Dennis Assanis
Keyword(s):  
Maximum Load ◽  
Heating Value ◽  
Hcci Combustion ◽  
Fuel Flow ◽  
Load Limit ◽  
Lower Heating Value ◽  
O2 Concentration ◽  
Negative Valve Overlap ◽  
Valve Overlap ◽  
Lower Heating

Homogeneous charge compression iginition (HCCI) combustion allows for the use of fuels with octane requirements below that of spark-ignited engines. A reference gasoline was compared with iso-octane and a low octane blend of gasoline and 40% n-heptane, NH40. Experiments were conducted on a single cylinder engine operating with negative valve overlap (NVO). The fuel flow rate per cycle was compensated based on the lower heating value to maintain a constant energy addition across fuels. Iso-octane and gasoline demonstrated similar maximum load, achieving a gross IMEPg of ~430 kPa, whereas the NH40 demonstrated an increased IMEPg of ~460 kPa. The NH40 could be operated at a later phasing compared with the higher octane fuels, and exhibited a shorter burn duration at a given fueling rate and phasing. These results could be due to compositional differences, as NH40 required less NVO compared to iso-octane and gasoline, leading to less thermal and compositional stratification, as well as a higher O2 concentration and less residual gas. Additionally, the NH40 fuel demonstrated a higher intermediate temperature heat release than the higher octane fuels, potentially contributing to the shorter burn duration. Overall, these results demonstrate clear benefits to NVO enabled HCCI combustion with low octane fuels.

A Cycle-to-Cycle Method to Predict HCCI Combustion Phasing

2013 ◽  
Author(s):  
Adam Vaughan ◽  
Stanislav V. Bohac
Keyword(s):  
Fuel Efficiency ◽  
Stability Limit ◽  
Low Temperature Combustion ◽  
Combustion Instabilities ◽  
Hcci Combustion ◽  
Crank Angle ◽  
Temperature Combustion ◽  
The Stability ◽  
Negative Valve Overlap ◽  
Valve Overlap

Homogeneous Charge Compression Ignition (HCCI) is a low temperature combustion strategy that simultaneously improves fuel efficiency and lowers engine-out NOx emissions. Unfortunately, broad usage of HCCI is hampered by combustion instabilities and a limited operation envelope. To help understand these limitations, this paper treats individual cylinders in a production four-cylinder engine as dynamical systems that iterate CA90 (the crank angle where 90% of net heat release is achieved) cycle-to-cycle as the engine operates in an unboosted, negative valve overlap HCCI combustion mode. This approach is shown to provide qualitative understanding of the stability limit bifurcation behavior, while also enabling quantitative cycle-to-cycle predictions of combustion phasing across a wide variety of transient and steady-state conditions, right up to complete misfire.

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