=Paper=
{{Paper
|id=Vol-452/paper-3
|storemode=property
|title=In-cylinder chemical species tomography for CI engines
|pdfUrl=https://ceur-ws.org/Vol-452/paper3.pdf
|volume=Vol-452
}}
==In-cylinder chemical species tomography for CI engines==
https://ceur-ws.org/Vol-452/paper3.pdf
In-cylinder Chemical Species Tomography for CI Engines
H. McCann * , E.M. Cheadle, J.L. Davidson, K.B. Ozanyan, N. Terzija and P. Wright
School of Electrical & Electronic Engineering
University of Manchester, Manchester, UK
High-speed Chemical Species Tomography (CST) using near-IR absorption has recently been demonstrated in a
multi-cylinder gasoline SI engine running on retail fuel. Many of the inherent advantages of the CST technique would
be even more marked in CI engines, for example in HCCI engines where mixture preparation involves residual spe-
cies, and in diesel engines where gross inhomogeneities over large spatial scales are the norm. On the basis of prac-
tical experience of CST in engines and in laboratory systems, this paper explores the potential for these applications
of the technique.
Introduction measurements, and beam array design for ade-
There is a long-term trend towards greater pre- quate spatial resolution. For high-speed imaging of
mixing of fuel and air in compression ignition (CI) hydrocarbon fuel in a gasoline SI engine cylinder,
engines. The most extreme case is the Homoge- the Manchester group has developed an imple-
neous Charge Compression Ignition (HCCI) engine mentation of Near-IR CST (Fig. 1) that has al-
[1]. Even in the “conventional” diesel engine, injec- lowed, to date, up to 32 simultaneous path-integral
tion sequences now lead to complex mixture de- measurements through the measurement subject
velopment processes. Moreover, the creation of [2-4]. This paper discusses the application of CST
engine-out pollutant species is of critical impor- to CI engines in projects that are now underway.
tance. These trends demand in-cylinder imaging of
chemical species in a variety of CI engine types. Key Features of Near-IR CST
The technique of Chemical Species Tomo- This technique offers direct sensitivity to the
graphy (CST) has recently emerged due to the target species, thus avoiding the use of artificial
maturing of Near-Infra-Red (Near-IR) opto- dopants. The Manchester system is based on con-
electronic technologies that were initially used in tinuous-wave diode lasers and photodiodes that
the communications industry: diode lasers, optical are inherently capable of rapid operation, enabling
fibres with mixers and splitters, and photodiodes. high-speed continuous imaging. The tomographic
The keys to exploiting these technologies are low approach requires optical access to the cylinder in
noise opto-electronic schemes for spectroscopic only one plane, and the use of fibre-based tech-
9/125 SM Fibers Uncollimated
Terminated by Re
nch ceiv 550/600 MM Fibers
GRIN Collimators Lau e
32 Photodiode Receivers
+ 64 Lock-In Amplifiers
1 by 32 Single Mode
nch
Rec
Fiber Optic Splitter
Lau
eiv
e
Measurement
Space
e
Lau
ceiv
nch
Re
Lau ei ve
nch Rec
Wavelength
Division
Multiplexer
160 kHz 160 kHz Data
Modulation
Reference
1550 nm Acquisition
Diode Laser System
1700 nm Clock
Diode Laser 90 kHz 90 kHz
For clarity, fibers are only shown for 2 (of 4) 8-beam projections
Fig. 1: Schematic diagram of first-generation Near-IR CST system.
* Corresponding author: h.mccann@manchester.ac.uk
Towards Clean Diesel Engines, TCDE2009
(a) (b) (c)
Fig. 2: (a) The 25 beams used in lab tests; (b) A double-plume phantom; (c) IMAGER reconstruction performance.
ºBTDC 42 39 36 33 30
Fig. 3: Tomographic images showing the development of fuel distribution in the period from 42˚ to 30˚ before TDC,
obtained using a 21-beam subset (1500rpm/1.5 bar BMEP load).
-ologies allows relatively small-scale and ro- particularly in terms of angular sampling [7]. Fig.
bust optical access. The Manchester system 2 shows some laboratory test results for pro-
offers great robustness to sprays and soot by pane plumes passing through the measurement
launching absorbed and reference wavelengths plane [7]. Fig. 3 shows example images ob-
(λ1 and λ2 respectively) along each beam path, tained when the engine was operated under
where the reference wavelength undergoes only conditions where a homogeneous fuel distribu-
scattering and beam-steering. tion was expected at ignition (15 ºBTDC) [6].
The first-generation system illustrated in Fig.
1, using simultaneous measurements along 32 Fuel Sprays and CST
beam paths, enabled the laboratory demonstra- The first-generation system achieved consid-
tion of high-speed CST of propane [3, 4] and erable success in imaging iso-octane fuel in a
iso-octane [5] at 3500 frames per second (fps). laboratory GDI set-up, despite operating at mar-
A second-generation system has been devel- ginally low laser modulation frequencies [5]. In
oped by the IMAGER consortium (Manchester, particular, it was found that the coarse features
Roush Technologies Ltd. and AOS Technology of a GDI spray could be imaged by using the
Ltd.) for application to multi-cylinder SI gasoline attenuation of the reference wavelength only.
engines (with λ2 = 1651nm), and implemented Fig. 4 illustrates this capability, clearly show-
on a 4-cylinder Ford Duratec PFI engine with 2.0 ing the hollow spray cone, which would be en-
L capacity (89mm bore) [6]. The IMAGER sys- hanced using model-dependent image recon-
tem is compatible with GDI sprays by the use of struction algorithms that are now available. In-
faster laser modulation, and incorporates a cylinder spray-shape imaging may thus be
unique OPtical Access Layer (OPAL) that achievable in running CI engines, with effectively
houses the launch and receive optics for 27 simultaneous measurement of gaseous fuel
beams that are irregularly arranged relative to distribution and its inhomogeneity. Such a study
each other. The balance between number and of CI engine combustion is to be explored in a
geometry of beams must be carefully optimized, new project with Shell in single-cylinder engines.
2.94 5.29 7.65 8.82 11.76 (ms after SOI)
Fig. 4: Tomographic images of the GDI spray cone after a 4ms iso-octane injection (red=high scattering).
Fig. 5: Calculated spectra of water at conditions relevant to HCCI (10% mole fraction water, pathlength 80 mm).
CST for HCCI research vated by the potential it offers for advances in
The combination of HCCI and variable 2/4- the underlying knowledge of CI engine proc-
stroke operation is being researched by a con- esses that determine combustion behaviour.
sortium of several universities, with Ricardo plc Initial CI applications are focused on single-
and Innospec Ltd. [8]. The Manchester CST cylinder optical engines.
technique is being adapted to image mixing In both engine types, there is great scope to
between combustion residuals and the fresh extend substantially the utility of the CST tech-
fuel/air charge, by imaging the distributions of nique to provide unique insights to help optimise
both water and hydrocarbon fuel. For small engine environmental performance.
molecules such as water, extensive databases
of spectroscopic parameters are available, e.g. Acknowledgements
in HITRAN [9], which are helpful for early-stage I would like to thank Prof. Gautam Kalghatgi
development of measurement systems. of Shell Global Solutions for instructive and
However, the IR transitions of interest can stimulating discussions concerning CI engines.
demonstrate complex behaviour as a function of
temperature and pressure. This is illustrated in References
Fig. 5, for the case of H2O under various condi- [1] H. Zhao (Ed.), Homogeneous charge compression
tions relevant to HCCI operation: Whilst very ignition (HCCI) and controlled auto ignition (CAI)
strong absorption is observed, the relatively engines for the automotive industry, Woodhead
narrow lines at low (i.e. intake) pressure show Publishing Ltd. (2007)
[2] S. J. Carey et al., Chemical Species Tomography
considerable temperature dependence, even by near infra-red absorption, Chem. Eng. J. 77,
over a range of only 100K. At high pressure (i.e. 111-118 (2000)
approaching ignition), each absorption feature is [3] F. P. Hindle et al., Measurement of gaseous hy-
composed of the broadened lineshapes of sev- drocarbon distribution by a Near Infra-Red absorp-
eral vibrational-rotational transitions and strong tion tomography system, J. Electronic Imaging 10,
temperature dependence is still evident. 593-600 (2001)
The choice of absorption wavelength for in- [4] P.Wright et al., Toward In-Cylinder Absorption
cylinder water measurement and imaging is Tomography in a Production Engine, Appl. Opt.
tractable, nevertheless, and also presents the 44, 6578-6592 (2005)
[5] F. P. Hindle et al., Near Infra-Red Chemical Spe-
potential to measure and image the distribution cies Tomography of Sprays of Volatile Hydrocar-
of temperature as well as concentration. bons, Technisches Messen 69, 352-357 (2002)
[6] P. Wright et al., High-speed Chemical Species
Conclusions Tomography in a multi-cylinder automotive engine,
The development of Near-IR CST for engine Chem. Eng. J., doi:10.1016/j.cej.2008.10.026
in-cylinder applications has reached the stage (2008)
where it can be applied confidently to single- [7] N. Terzija et al., Image optimisation for chemical
and multi-cylinder gasoline SI engines for fuel species tomography with an irregular and sparse
beam array, Meas. Sci. Technol. 19 094007(2008)
imaging. In the multi-cylinder case, robust fibre-
[8] See grant ref. EP/F05825X/1 at www.epsrc.ac.uk
based optical access has been demonstrated. [9] Rothman et al, The HITRAN 2004 molecular spec-
The challenges posed in adapting CST to CI troscopic database, J. Quantum Spectrosc. 96,
engines are significant, but are strongly moti- 139–204 (2005)