Modeling the Effects of Steam-Fuel Reforming Products on Homogeneous Charge Compression Ignition of n-Heptane

2009 ◽  
Author(s):  
Francisco Posada ◽  
Nigel N. Clark ◽  
Aleksandr Kozlov ◽  
Martin Linck ◽  
Dmitri Boulanov ◽  
...  
Keyword(s):  
Species Composition ◽  
Heat Release ◽  
Homogeneous Charge Compression Ignition ◽  
Zone Model ◽  
Compression Ignition ◽  
Ignition Timing ◽  
Fuel Reforming ◽  
Total N ◽  
Temperature Heat ◽  
Homogeneous Charge

Homogeneous Charge Compression Ignition (HCCI) offers benefits of high efficiency with low emissions, but suffers load range limitations and control issues. A method to improve control of HCCI was numerically investigated based on two separate fuel streams with different autoignition characteristics to regulate timing and heat release at specific operational conditions. In this numerical study n-heptane was selected as the primary fuel, and the secondary fuel was defined as a reformed product of n-heptane (RG). The reformed fuel species composition was experimentally determined based on steam/n-heptane reforming process at a steam/carbon mole ratio of 2:1. In addition to H2 and CO, the reformed fuel stream was composed of CH4, CO2, H2O and non-reformed n-heptane. A single zone model using a detailed chemical kinetic mechanism was implemented on CHEMKIN to study the effects of base fuel and steam-fuel reforming products on the ignition timing and heat release characteristics. The study was performed considering the reformed fuel species composition at total n-heptane conversion (stoichiometric) and also at the composition corresponding to a specific set of operational reforming temperatures. The computational model confirmed that the reformed products have a strong influence on the low temperature heat release (LTHR) region, affecting the onset of the high temperature heat release (HTHR). The ignition timing was proportionally delayed with respect to the baseline fuel case when higher concentrations of reformed gas were used.

Effects of N2 and CO2 mixing on ignition and combustion in a homogeneous charge compression ignition engine operated on dimethyl ether

2005 ◽  
Vol 6 (5) ◽  
pp. 423-431 ◽  
Author(s):  
W Sahashi ◽  
A Azetsu ◽  
C Oikawa
Keyword(s):  
Heat Release ◽  
Co Oxidation ◽  
Homogeneous Charge Compression Ignition ◽  
Exhaust Gas ◽  
Compression Ignition ◽  
Ignition Timing ◽  
Cool Flames ◽  
Combustion Duration ◽  
Co Emission ◽  
Homogeneous Charge

The control of ignition timing and combustion duration over a wide range of engine speeds and loads in a homogeneous charge compression ignition (HCCI) engine is one of the barriers to the realization of this type of engine. Application of exhaust gas recirculation (EGR) is a promising option to control ignition timing, extend combustion duration, and suppress knock-like combustion. In this study, the effects of the mixing of N2 and CO2, major components of exhaust gas, with the fuel-air mixture on the heat release of the cool flames and the emission characteristics of CO were investigated by experiment and computation. The heat release of the cool flames was reduced with N2 mixing; however, it increased with CO2 mixing. From the systematic experiments and chemical kinetic computations, it was confirmed that the amount of heat release from the cool flames depends strongly on the concentration of O2 at the onset of cool flame. The dominant pathway for CO oxidation is the reaction of CO + OH = CO2 + H, where the H atoms produced react with O2 molecules and produce OH + O or HO2. The CO oxidation becomes active as the branching rate to OH + O is increasing. However, the branching rate to HO2 was increased with the addition of CO2 into the mixture, resulting in higher CO emission. Though the mixing of CO2 is effective in suppressing knock-like combustion owing to its small specific heat ratio and large heat capacity, it has an inferior effect on CO emission.

Characterizing the cyclic variability of ignition timing in a homogeneous charge compression ignition engine fuelled with n-heptane/iso-octane blend fuels

2008 ◽  
Vol 9 (5) ◽  
pp. 361-397 ◽  
Author(s):  
M Shahbakhti ◽  
C R Koch
Keyword(s):  
Equivalence Ratio ◽  
Homogeneous Charge Compression Ignition ◽  
Coolant Temperature ◽  
Cyclic Variation ◽  
Compression Ignition ◽  
Ignition Timing ◽  
Compression Ignition Engine ◽  
Hcci Combustion ◽  
Cyclic Variations ◽  
Homogeneous Charge

The cyclic variations of homogeneous charge compression ignition (HCCI) ignition timing is studied for a range of charge properties by varying the equivalence ratio, intake temperature, intake pressure, exhaust gas recirculation (EGR) rate, engine speed, and coolant temperature. Characterization of cyclic variations of ignition timing in HCCI at over 430 operating points on two single-cylinder engines for five different blends of primary reference fuel (PRF), (iso-octane and n-heptane) is performed. Three distinct patterns of cyclic variation for the start of combustion (SOC), combustion peak pressure ( Pmax), and indicated mean effective pressure (i.m.e.p.) are observed. These patterns are normal cyclic variations, periodic cyclic variations, and cyclic variations with weak/misfired ignitions. Results also show that the position of SOC plays an important role in cyclic variations of HCCI combustion with less variation observed when SOC occurs immediately after top dead centre (TDC). Higher levels of cyclic variations are observed in the main (second) stage of HCCI combustion compared with that of the first stage for the PRF fuels studied. The sensitivity of SOC to different charge properties varies. Cyclic variation of SOC increases with an increase in the EGR rate, but it decreases with an increase in equivalence ratio, intake temperature, and coolant temperature.

A new heat release rate (HRR) law for homogeneous charge compression ignition (HCCI) combustion mode

2009 ◽  
Vol 29 (17-18) ◽  
pp. 3654-3662 ◽  
Author(s):  
Miguel Torres García ◽  
Francisco José Jiménez-Espadafor Aguilar ◽  
Tomás Sánchez Lencero ◽  
José Antonio Becerra Villanueva
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Homogeneous Charge Compression Ignition ◽  
Compression Ignition ◽  
Combustion Mode ◽  
Hcci Combustion ◽  
Homogeneous Charge

Combustion and emission characteristics of a homogeneous charge compression ignition engine

2005 ◽  
Vol 219 (9) ◽  
pp. 1133-1139 ◽  
Author(s):  
Hu Tiegang ◽  
Liu Shenghua ◽  
Zhou Longbao ◽  
Zhu Chi
Keyword(s):  
Heat Release ◽  
Homogeneous Charge Compression Ignition ◽  
Cetane Number ◽  
Pressure Rise ◽  
Operating Conditions ◽  
Emission Characteristics ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Hcci Engine ◽  
Homogeneous Charge

Dimethyl ether (DME) is a kind of fuel with high cetane number and low evaporating temperature, which is suitable for a homogeneous charge compression ignition (HCCI) engine. The combustion and emission characteristics of an HCCI engine fuelled with DME were investigated on a modified single-cylinder engine. The experimental results indicate that the HCCI engine combustion is a two-stage heat release process. The engine load or air-fuel ratio has significant effects on the maximum cylinder pressure and its position, the shape of the pressure rise rate and the heat release rate. The engine speed has little effect. A DME HCCI engine is smoke free, with zero NOx and low hydrocarbon and CO emissions under the operating conditions of 0.25–0.30 MPa brake mean effective pressure.

An accelerated multi-zone model for engine cycle simulation of homogeneous charge compression ignition combustion

2013 ◽  
Vol 14 (5) ◽  
pp. 416-433 ◽  
Author(s):  
Janardhan Kodavasal ◽  
Matthew J McNenly ◽  
Aristotelis Babajimopoulos ◽  
Salvador M Aceves ◽  
Dennis N Assanis ◽  
...  
Keyword(s):  
Homogeneous Charge Compression Ignition ◽  
Zone Model ◽  
Compression Ignition ◽  
Cycle Simulation ◽  
Compression Ignition Combustion ◽  
Engine Cycle ◽  
Homogeneous Charge

Modelling and Simulation of Homogeneous Charge Compression Ignition Engine Fueled by Biodiesel

2018 ◽  
Author(s):  
Meshack Hawi ◽  
Mahmoud Ahmed ◽  
Shinichi Ookawara
Keyword(s):  
Heat Release ◽  
Compression Ratio ◽  
Homogeneous Charge Compression Ignition ◽  
Internal Combustion ◽  
Operating Conditions ◽  
Emission Characteristics ◽  
Compression Ignition ◽  
Hcci Engine ◽  
Hcci Engines ◽  
Homogeneous Charge

Homogeneous charge compression ignition (HCCI) is a combustion technology which has received increased attention of researchers in the combustion field for its potential in achieving low oxides of nitrogen (NOx) and soot emission in internal combustion (IC) engines. HCCI engines have advantages of higher thermal efficiency and reduced emissions in comparison to conventional internal combustion engines. In HCCI engines, ignition is controlled by the chemical kinetics, which leads to significant variation in ignition time with changes in the operating conditions. This variation limits the practical range of operation of the engine. Additionally, since HCCI engine operation combines the operating principles of both spark ignition (SI) and compression ignition (CI) engines, HCCI engine parameters such as compression ratio and injection timing may vary significantly depending on operating conditions, including the type of fuel used. As such, considerable research efforts have been focused on establishing optimal conditions for HCCI operation with both conventional and alternative fuels. In this study, numerical simulation is used to investigate the effect of compression ratio on combustion and emission characteristics of an HCCI engine fueled by pure biodiesel. Using a zero-dimensional (0-D) reactor model and a detailed reaction mechanism for biodiesel, the influence of compression ratio on the combustion and emission characteristics are studied in Chemkin-Pro. Simulation results are validated with available experimental data in terms of incylinder pressure and heat release rate to demonstrate the accuracy of the simulation model in predicting the performance of the actual engine. Analysis shows that an increase in compression ratio leads to advanced and higher peak incylinder pressure. The results also reveal that an increase in compression ratio produces advanced ignition and increased heat release rates for biodiesel combustion. Emission of NOx is observed to increase with increase in compression ratio while the effect of compression ratio on emissions of CO, CO2 and unburned hydrocarbon (UHC) is only marginal.

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