Indiana University-Purdue University Indianapolis (IUPUI) / Ignition by a jet of hot combustion product gas injected into a premixed combustible mixture from a separate pre-chamber is a complex phenomenon with jet
penetration, vortex generation, flame and shock propagation and interaction. It has
been considered a useful approach for lean, low-NOx combustion for automotive engines, pulsed detonation engines and wave rotor combustors. The hot-jet ignition
constant-volume combustor (CVC) rig established at the Combustion and Propulsion
Research Laboratory (CPRL) of the Purdue School of Engineering and Technology
at Indiana University-Purdue University Indianapolis (IUPUI) is considered for numerical study. The CVC chamber contains stoichiometric methane-hydrogen blends,
with pre-chamber being operated with slightly rich blends. Five operating and design
parameters were investigated with respect to their eff ects on ignition timing. Di fderent pre-chamber pressure (2, 4 and 6 bar), CVC chamber fuel blends (Fuel-A: 30%
methane + 70% hydrogen and Fuel-B: 50% methane + 50% hydrogen by volume), active radicals in pre-chamber combusted products (H, OH, O and NO), CVC chamber
temperature (298 K and 514 K) and pre-chamber traverse speed (0.983 m/s, 4.917
m/s and 13.112 m/s) are considered which span a range of fluid-dynamic mixing and
chemical time scales. Ignition delay of the fuel-air mixture in the CVC chamber is
investigated using a detailed mechanism with 21 species and 84 elementary reactions
(DRM19). To speed up the kinetic process adaptive mesh refi nement (AMR) based
on velocity and temperature and multi-zone reaction technique is used.
With 3D numerical simulations, the present work explains the e ffects of pre-chamber pressure, CVC chamber initial temperature and jet traverse speed on ignition for a speci fic set of fuels. An innovative post processing technique is developed
to predict and understand the characteristics of ignition in 3D space and time.
With the increase of pre-chamber pressure, ignition delay decreases for Fuel-A
which is the relatively more reactive fuel blend. For Fuel-B which is relatively less
reactive fuel blend, ignition occurs only for 2 bar pre-chamber pressure for centered
stationary jet. Inclusion of active radicals in pre-chamber combusted product decreases the ignition delay when compared with only the stable species in pre-chamber
combusted product. The eff ects of shock-flame interaction on heat release rate is observed by studying flame surface area and vorticity changes. In general, shock-flame
interaction increases heat release rate by increasing mixing (increase the amount of
deposited vorticity on flame surface) and flame stretching. The heat release rate is
found to be maximum just after fast-slow interaction.
For Fuel-A, increasing jet traverse speed decreases the ignition delay for relatively
higher pre-chamber pressures (6 and 4 bar). Only 6 bar pre-chamber pressure is
considered for Fuel-B with three di fferent pre-chamber traverse speeds. Fuel-B fails
to ignite within the simulation time for all the traverse speeds.
Higher initial CVC temperature (514 K) decreases the ignition delay for both fuels
when compared with relatively lower initial CVC temperature (300 K). For initial
temperature of 514 K, the ignition of Fuel-B is successful for all the pre-chamber
pressures with lowest ignition delay observed for the intermediate 4 bar pre-chamber
pressure. Fuel-A has the lowest ignition delay for 6 bar pre-chamber pressure.
A speci fic range of pre-chamber combusted products mass fraction, CVC chamber
fuel mass fraction and temperature are found at ignition point for Fuel-A which were
liable for ignition initiation. The behavior of less reactive Fuel-B appears to me more
complex at room temperature initial condition. No simple conclusions could be made
about the range of pre-chamber and CVC chamber mass fractions at ignition point.
| Identifer | oai:union.ndltd.org:IUPUI/oai:scholarworks.iupui.edu:1805/7960 |
| Date | January 2015 |
| Creators | Khan, Md Nazmuzzaman |
| Contributors | Nalim, Mohamed Razi, Yu, Whitney, Zhu, Likun |
| Source Sets | Indiana University-Purdue University Indianapolis |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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