Exp Fluids (2015) 56:3
Laser‑induced incandescence measurements in a ﬁred diesel
engine at 3 kHz
I. G. Boxx · O. Heinold · K. P. Geigle
Received: 25 August 2014 / Revised: 11 November 2014 / Accepted: 18 November 2014 / Published online: 10 January 2015
© Springer-Verlag Berlin Heidelberg 2014
Compression ignition diesel engines are an efﬁcient and
widely used technology in the transportation industry.
Increasingly, strict regulation of both nitric oxide (NOx)
and soot emissions from diesel engines has led to a number
of innovations in engine technology, including new injec-
tor and piston geometries, injection strategies, exhaust gas
recirculation, and swirl-enhanced in-cylinder mixture prep-
aration. The complex mixture preparation and combustion
strategies on which these new technologies rely depend
strongly upon a deep fundamental understanding of the
physical processes relating to soot formation, agglomera-
tion, breakup, and oxidation.
Laser-based imaging diagnostics such as laser-induced
incandescence (LII) are a key tool in understanding in-
cylinder soot dynamics (Eckbreth 1977; Melton 1984). In
the LII measurement technique, soot particles are rapidly
heated to ≥4,000 K using a high-intensity pulsed laser, and
the resulting incandescence is captured on a photo sen-
sor, typically a photomultiplier tube or an intensiﬁed cam-
era. The LII technique can produce both point and planar,
in situ measurements of soot volume fraction and particle
size. It has been used to study soot distributions in labora-
tory-scale test ﬂames (Shaddix and Smyth 1996; Will et al.
1996), automotive engines (Dec et al. 1991; Bougie et al.
2006; Kock et al. 2006), high-pressure combustors (Braun-
Unkhoff et al. 1998; Hofmann et al. 2003; Lammel et al.
2007), and engine exhausts (Snelling et al. 2000; Black
and Johnson 2010). A thorough review of the LII technique
can be found in (Santoro and Shaddix 2002; Schulz et al.
A key limitation of LII stems from its need for high-
intensity pulsed laser illumination which has, until recently,
restricted it to temporally uncorrelated, single-shot or
Abstract Laser-induced incandescence (LII) was per-
formed at 3 kHz in an optically accessible cylinder of a
ﬁred diesel engine using a commercially available diode-
pumped solid-state laser and an intensiﬁed CMOS camera.
The resulting images, acquired every 3° of crank angle,
enabled the spatiotemporal tracking of soot structures dur-
ing the expansion/exhaust stroke of the engine cycle. The
image sequences demonstrate that soot tends to form in thin
sheets that propagate and interact with the in-cylinder ﬂow.
These sheets tend to align parallel to the central axis of the
cylinder and are frequently wrapped into conical spirals
by aerodynamic swirl. Most of the soot is observed well
away from the cylinder walls. Quantitative soot measure-
ments were beyond the scope of this study but the results
demonstrate the practical utility of using kHz-rate LII to
acquire ensemble-averaged statistical data with high crank
angle resolution over a complete engine cycle. Based on
semi-quantitative measures of soot distribution, it was pos-
sible to identify soot dynamics related to incomplete charge
exchange. This study shows that long-duration, multi-kHz
acquisition rate LII measurements are viable in a ﬁred die-
sel engine with currently available laser and camera tech-
nology, albeit only in the expansion and exhaust phase of
the cycle at present. Furthermore, such measurements yield
useful insight into soot dynamics and therefore constitute
an important new tool for the development and optimiza-
tion of diesel engine technology.
I. G. Boxx (*) · K. P. Geigle
Deutsches Zentrum für Luft- und Raumfahrt e.V.,
Pfaffenwaldring 38-40, 70569 Stuttgart, Germany
Robert Bosch GmbH, Robert-Bosch-Platz 1, 70839 Gerlingen,