KCFP_Annual_Report_2010.pdf

KCFP
Kompetenscentrum Förbränningsprocesser
Centre of Competence Combustion Processes
Annual Report 2010
Faculty of Engineering, LTH
Lund University

KCFP
Centre of Competence Combustion Processes
The Centre of Competence Combustion Processes, KCFP, started July 1 1995.
The main goal of this centre is to better understand the combustion process in internal
combustion engines. Of particular interest are the combustion processes with low enough
temperature to suppress formation of NOx and particulates, PM, often called Low Temperature
Combustion, LTC or Homogeneous Charge Compression Ignition, HCCI.
The Centre of Competence Combustion Processes has a budget of 22.25 MSEK per year.
This is roughly one third each from the Swedish Energy Agency, STEM, Lund University and
the Industry.
CONTENTS
1. The Partially Premixed Combustion Project 6
1.1 PPC - Heavy Duty 6
1.2 PPC - Light Duty 10
1.3 Optical Diagnostics 12
1.4 Combustion Modelling 16
1.5 PPC Fuels 18
1.6 Combustion Control 20
2. The Generic Diesel Project 23
2.1 Analysis of the Initial Soot Formation During an EGR Sweep 23
2.2 Post-Injection Effects on Near-Injector Over-Lean Mixtures
and UHC Emissions 24
2.3 Optical Diagnostics Development 26
3. The Gas Engine Project 30
3
INDUSTRY
PARTNERS
Volvo Cars
Volvo Powertrain
Volvo Penta
Saab
Scania
Toyota
Caterpillar
Cargine
Chevron
Finnveden
Hoerbiger
Wärtsilä
The Swedish Gas
Centre, SGC

Associate
Professor
Per Tunestål
Supervisor for:
CC and SIGE
KCFP
ORGANISATION
BOARD
Sören Udd, Volvo Powertrain
Börje Grandin, Volvo Cars
Annika Kristoffersson, Saab (Chair)
Jonas Hoffstedt, Scania CV
Professor
Marcus Aldén
Supervisor for:
PPC and
GenDies
Associate
Professor
Mattias Richter
Supervisor for:
PPC and
GenDies
Professor
Rolf Johansson
Supervisor for:
CC
DIRECTOR
Professor
Bengt Johansson
Supervisor for:
PPC
Assistant
Professor
Öivind Andersson
Supervisor for:
GenDies
4
Ulla Holst, LTH
Ida Truedsson, LTH
(student representative)
Professor
Xue-Song Bai
Supervisor for:
CM
ADMINISTRATOR
Maj-Lis Roos
Assistant
Professor
Martin Tunér
Supervisor for:
Fuel
ADMINISTRATOR
Elna Andersson

Vittorio Manente
PhD Student
1. The Partially Premixed Combustion Project
Partially Premixed Combustion, PPC, is a combustion process between Homogeneous
Charge Compression Ignition, HCCI and the classical diffusion controlled diesel combustion.
With PPC it is possible to moderate the charge stratification and thus control the
burn rate better than with HCCI. In comparison to classical diesel combustion the NOx and
particulates can be suppressed with orders of magnitude. KCFP has five different but linked
subprojects on PPC.
In the Heavy Duty PPC subproject, the first Ph.D. student, Vittorio Manente, has been running
a Scania D13 truck size diesel engine with PPC using diesel fuel as well as gasoline in
the 69-99 octane range. With gasoline it was possible to run from idle up to 30 bar IMEP
even though only 26 bar was reported. Vittorio presented his thesis in September 2010 and
was replaced by Peter Andersson. Peter has been focusing on ethanol as PPC fuel and initial
tests has shown great potential with much less soot. In The Light Duty PPC project, PPC-LD,
the Ph.D. student Patrick Borgqvist has been working with SI and HCCI reference tests in the
low load regime. He has also designed a combustion chamber that should enable PPC combustion
with the active valve train from Cargine. In the PPC-Fuels subproject the student,
Hadeel Solaka, has been working with fuel and combustion interactions with the same fuels
previously used in the PPC-HD project. Larger than expected differences between Heavy
Duty and Light Duty engine geometries were found. The PPC optical diagnostics have been
in a build-up phase with of two kind of activities 2010. A new Scania D13 optical engine design
has been developed and machined but due to delays in the lab, it has not been up and
running during 2010 but will do so 2011. Due to the delay, the optical diagnostics activities
2010 have been performed in stationary test rigs instead. The PPC modelling subproject
is based on the HCCI and SACI models developed in the previous phase of KCFP. The PPC
model with LES started with using gaseous jet modelling and will eventually move to include
also sprays. The fundamental DNS simulations of hydrogen spray and combustion can
give additional insight on the PPC type of combustion. The former controls project has due
to budget constraints been reduced in the current phase of KCFP, thus less results can also
be expected. Even so, the PPC control project has done mode switch SI-HCCI-SI using model
based control in the PPC-LD engine having the fully flexible valve system. The developed
control strategies can also be useful for PPC.
1.1. PPC - Heavy Duty
Gasoline PPC Combustion in Scania D13 Engine
During 2010 tests with a Scania D13 engine were performed using various types of gasolines
with a range of octane numbers. Figure 1 shows the resulting operating range as a function
of octane number with fixed low inlet temperature. For low ON it is possible to use PPC
mode of combustion from idle to 26 bar IMEP but with a octane number above 70 low load
becomes a problem. With commercial gasoline with RON in the 95-99 range the low limit s
15 bar. How to enable also low load operation will be investigated in the future.
6

Figure 1: Load range with inlet temperature of 25C.
Figure 2: Emissions as a function of load for two low octane gasoline in comparison to future
emission limits in US and Europe.
7

Peter Andersson
PhD Student
Figure 2 shows that the emission levels with low octane gasoline can be below the legal limits
(except for Pm at higher loads). With some fine tuning and optimization also PM could be
within target.
Tests with modified combustion chamber, spray umbrella angle and swirl levels were performed
in order to repeat the 2008-2009 results in the former Scania D12 geometry. Swirl
was increased to 3.7, spray angle set to 120 degrees and a piston with 14.3 nominal compression
ratio was installed. An improvement in soot-NOx trade-off was found with increased
swirl but the combustion chamber shape was found less suitable with the narrow spray angle
of 120 degrees. A new combustion chamber must thus be designed and evaluated during
2011.
Ethanol PPC Results
Figure 3: Combustion chambers and resulting soot-NOx trade-off
with increased swirl level (HS) at loads 50-100% at A speed.
As with the gasoline PPC the whole load range can be optimized for low emissions and relatively
high efficiency with 40-45% of EGR and low λ using ethanol as fuel. The main diffrence
to gasoline is that no soot is formed

Figure 4: Heat release, injection signal and cylinder pressure for low and medium load ethanol PPC.
Figure 5: Combustion efficiency.
Even though a low lambda can be used with ethanol without producing soot a high level of
EGR is needed to slow down the combustion and prevent excessive the pressure rise rate. For
low loads the EGR level has a minor influence while it is of great interest for middle and high
loads.
Planned activities
For 2011, the current campaign with 95% ethanol is to be finished and investigations with
ethanol and λ = 1 is in the pipeline. Further work is to modify the engine with a new combustion
chamber, i.e. a new piston, to investigate how this influence the efficiency.
9

Patrick Borgqvist
PhD Student
1.2 PPC - Light Duty
Introduction
Gasoline partially premixed combustion is a promising way to achieve simultaneous high efficiency
and low soot and NOx emissions in a diesel engine. Running on gasoline, there is
a potential to get adequate premixing of fuel and air to avoid soot formation. With proper
fuel injection strategy, the combustion is controlled so that excessive heat-release rates are
avoided, which is one of the problems with HCCI combustion at higher loads.
The problem with gasoline partially premixed combustion is the limeted operating region
running with higher octane number fuels. See Figure 1. The purpose of this project is to
increase the attainable operating region and increase the understanding of the combustion
process. The approach is to use a variable valve timing system and different fuel injection
strategies. At a later stage, laser diagnostics will be applied to get increased knowledge and
detailed information of the combustion.
During the first year, an extensive pre-study has been carried out. The purpose is to investigate
and compare spark ignited and HCCI combustion with high octane number fuel (RON95)
using variable valve timings within the target area (circled in the diagram).
Figure 6: Experimental engine and piston crown.
Experimental Setup
The research engine is based on a Volvo D5. It has been modified to run on only one of the five
cylinders, and is equipped with a Cargine fully flexible pneumatic variable valve train system,
a spark plug and both a direct injection and port-fuel injection system. At the first stage, only
the port-fuel injection system has been used. The piston crown had to be modified in order to
get valve clearance around top-dead centre. The piston crown design was inspired by a design
in an article from Toyota [1]. The research engine and piston crown can be seen in Figure 6..
10

Figure 7: Collected rate of heat release curves, operating point 1500 rpm, 3.5 bar IMEP net.
Results
The engine was run port-fuel injected with gasoline (RON95) at engine speeds 1500 rpm and
2000 rpm. Spark ignited and HCCI combustion using different variable valve timings strategies
were compared; spark ignited combustion using conventional valve timings and a throttle to
control load (SI Throttle); spark ignited combustion using late intake valve closing timing (SI
LIVC); spark ignited combustion using early intake valve closing (SI EIVC); HCCI combustion using
negative valve overlap (HCCI NVO); HCCI combustion using retarded closing of the exhaust
valve (HCCI Reb 1); HCCI combustion using a second opening of the exhaust valve late during
the intake stroke (HCCI Reb 2); HCCI with conventional valve timings and pre-heated air. Combustion
timings were optimized for maximum indicated efficiency for each strategy.
The collected rate of heat-release curves from operating point 3.5 bar IMEPnet is seen in Figure
7. The apparent difference between spark ignited combustion and HCCI combustion are
clearly seen. With Partially premixed combustion the goal is to achieve a curve which would
be somewhere in between the spark ignited and HCCI curves. This would be obtained with
a more advanced injection strategy. With a controllable combustion, excessive heat-release
rates can be avoided, and high efficiency with acceptable pressure rise rates can be obtained.
11

Figure 8: Net indicated efficiency, operating point 1500 rpm.
The net indicated efficiencies are summarized in Figure 8. The relative improvement in efficiency
is up to approximately 25% comparing the HCCI Rebreathing strategies with the spark
ignited strategies. The HCCI negative valve overlap strategy suffers mainly from lower gasexchange
efficiency and the pre-heated air HCCI strategy suffers from low combustion efficiency.
References
[1] Improvement of Diesel Engine Performance by Variable Valve Train System, T. Tomoda,
T. Ogawa, H. Ohki, T. Kogo, Dr. K. Nakatani, E. Hashimoto, Toyota Motor Corporation, Japan,
30. Internationales Wiener Motorensymposium 2009
1.3 Optical Diagnostics
Further work on multiple scattering suppression for spray imaging
Structured Laser Illumination Planar Imaging, SLIPI, is a planar imaging technique capable of
suppressing multiple scattering. The principle of the technique is to use a laser sheet which
is spatially modulated in intensity instead of a homogeneous laser sheet. This modulation,
which has a sinusoidal pattern, acts as a ”finger print” allowing the singly scattered photons
to be recognized, as they will scatter accordingly. In contrast, photons which are scattered
several times within the sample before detection appear as a position-dependent intensity
noise on the recorded image and will not follow the modulation pattern. To extract the single
scattering from the multiple light scattering intensity, the method consists in extracting the
amplitude of the modulated component. This does, however, require three modulated images
to be recorded for each event.
Imaging of optical depth
The optical depth describes the turbidity of a sample and is usually measured by illuminating
the medium with a laser beam and to measure the reduction of light in the far field. The
undesired detection of multiple scattering makes imaging of optical depth extremely challenging
and the resulting value is often underestimated using conventional imaging methods.
By combining structured illumination with transmission imaging it is possible to visualize the
optical depth in two dimensions while minimizing the influence from multiple scattered light.
Figure 9 shows an example of such a measurement.
12

Figure 9: Two-dimensional measurements of optical dept in a water spray. The image to the left shows
the results obtained with conventional technique and the image to the right is obtained using SLIPI to
suppress multiply scattered light. Note the underestimation that occurs when scattered light taken into
account.
3D imaging with correction for signal losses
Imaging of turbid media, such as sprays, is challenging not only because of multiple scattering
but also because of losses of both the light from the light source as well as the signal itself.
Figure 10 shows a three-dimensional view of an aerated spray corrected for these losses of
light. This was made possible by measuring the optical depth simultaneously imaging the
sample at different positions.
Figure 10: Three-dimensional view of an aerated water spray that has been corrected for the above
mentioned intensity losses.
13

First test of SLIPI in a diesel spray
The first preliminary test of applying the SLIPI technique to a diesel spray has been conducted.
The tests were performed in a spray chamber with an ambient pressure of 19 bar and the injection
pressure was 600 bar. Commercial diesel fuel was used throughout the test. Although
the conditions were not replicating true in-cylinder conditions, the results are promising for
future applications in engines.
Figure 11: Mie scattering at different times after start of injection (TSOI) recorded with conventional
sheet imaging (above) and SLIPI (below). Injection pressure 600 bar, chamber ambient pressure 19 bar.
Note the significant amount of multiple scattered light in the conventional images.
Wall temperature measurements
As outlined in the previous report there is an interest in measuring the in-cylinder wall temperature.
This is especially the case when running combustion systems with high pressure
rise rates such as HCCI and PPC. There is a possibility that the induced pressure oscillations
can rupture the thermal boundary layer and thus cause a severe increase in heat transfer to
the relatively cold wall. Such phenomena could be investigated using thermographic thermometry.
The surface of interest is coated with a thin layer of a suitable thermo sensitive
material often referred to as a thermographic phosphor. Then the coating is illuminated with
laser radiation and shortly thereafter, when the excited phosphor relaxes, light is emitted. This
resulting radiation from most thermographic phosphors has a duration and spectral characteristics
that is dependent on the temperature. Measurements of the signal decay generally
results in a temperature reading with higher precision compared to corresponding spectral
measurements. Decay times are measured using photo multiplier tubes (PMT) which limits
this approach to point temperature measurements. Spectral investigations are often based
on taking the ratio between two recordings performed at two different wavelengths. This can
be performed using high sensitivity cameras which enable two-dimensional measurements.
These techniques have been applied in engines before both within kcfp and at other research
centers. Thermographic phosphors have proven to be a robust technique capable of delivering
qualitative and quantitative data also when applied in harsh environments such as engines.
However, what has been lacking is detailed knowledge about the precision and accuracy of
the measurement technique.
14

The two main approaches (decay time and spectral) are both in need of thorough studies in
order to reach a level where absolute temperatures can be presented with reliable error bars.
The latter is highly important if small temperature variations on an in-cylinder wall should be
possible to detect in a trustful manner. An extensive effort has been focused on refining the
two-dimensional temperature measurement technique in order to bring it to the desired level.
This, still ongoing, study includes detailed investigations on: reproducibility, spectral ratio
dependence of phosphorescence intensity, laser intensity, detector gain, detector integration
time and phosphor layer thickness. All these parameters must be taken into account if real
quantitative data with known measurement errors should be possible. A fundamental, but
far from trivial, requirement is that the spectral intensity ratio should depend on the surface
temperature only. This means that even if the original measurements performed at two different
wavelengths should show intensity variations due to laser intensity variations or variations
in phosphor concentration, the resulting ration between these two images should only
reflect temperature, se example in Figure 12. So far the investigations have revealed a much
greater complexity than initially expected. However, if carried out carefully the thermographic
phosphor technique shows great potential of reaching a measurement precision of only a few
percent also for 2D temperature probing and that is truly outstanding for a probing technique
with such high temporal resolution.
Figure 12: For the ratio method two images (upper two) are detected through different optical filters and then
the ratio is calculated. This resulting ratio image (above) holds the temperature information. In this particular
case it can clearly be seen how variations in the raw data, caused by laser intensity variations, are canceled out
when the ratio is calculated. This is unfortunately not always the case, and if reliable temperature data is to be
retrieved all the above mentioned parameters must be considered.
15

Rickard Solsjö
PhD Student
Tobias Joelsson
PhD Student
1.4 Combustion Modelling
Introduction
The goal of the PPC modelling project is to use high fidelity simulation methods to simulate
to a rather detailed level the spray injection, the gas jet mixing with ambient EGR and air, and
the ignition/reaction fronts propagation in PPC engines. Modeling tools developed in KCFP
phase 5 and CeCOST 3 are used for the PPC studies. Specially, large eddy simulation (LES) will
be used, instead of Reynolds averaged Navier-Stokes (RANS) modeling, as LES can capture the
most energetic turbulence structures down to the Taylor micro-scales, and only the sub-scale
turbulence transport for mass, momentum and energy needs to be modeled. This way the
most important phenomena in PPC are simulated properly, such as the vortex shedding and
Kelvin-Helmholtz instability associated with the gas jet and the liquid spray injection, the gas
jet flow interaction with piston wall, etc. For the high speed spray injection study an open
source code OpenFoam is used to take into account the compressibility effect. In addition to
the available tools developed previously, particular flow/chemistry coupling models for PPC
ignition and combustion wave propagation needs to be revisited and validated. This involves
study of PPC using direct numerical simulation (DNS). DNS is developed under generic conditions
for simple fuels such as hydrogen. The modeling project is operated in close collaboration
with the engine experiments and laser diagnostics activities within KCFP, to gain maximum
synergy effect to improve the understanding of the fundamental physical and chemical
processes involved in PPC, and to be able to explain phenomena found in the engine tests. The
DNS data is used to validate different modeling concepts, e.g. progress variable based ignition
tabulation approach and multi-zone chemistry mapping (MZCM) approach.
Large eddy simulation of high speed gaseous fuel injection
As a first step we investigate the effect of high speed vapor fuel injection on fuel stratification
and fuel-air mixing, at different injection and ambient conditions. To focus the effort, only the
mixing of fuel and air inside a vessel has been considered. The work is conducted using LES
with an open source CFD-software OpenFoam. To achieve improved understanding on the behavior
of the fuel/air mixing, more attention has been placed on the physics at the early stages
of fuel injection. A constant volume enclosure similar to the combustion vessel developed at
Sandia and Lund University has been studied.
(a)(a) (a)(b) (a)(c)
Figure 13: Instantaneous distribution of mass fraction of fuel in the combustion vessel; (a) 1100 bar
injection pressure and ambient density of 22.8kg/m 3 , (b) 2000 bar injection pressure and ambient density
of 22.8kg/m 3 , (c) 2000 bar injection pressure and ambient density of 40kg/m 3 .
16

Figure 13 shows the effect of injection pressure and ambient density on the mixing of fuel
and the ambient air. With lower injection pressure and lower density (case a) the instability of
the jet develops later and mixing of the fuel with ambient is slower; increasing the injection
pressure leads to an earlier onset of Kelvin-Helmholtz instability and enhanced mixing (case
b); increasing density, however, leads to a delay of instability and slower mixing (case c).
Figure 14. Probability density function (PDF) of fuel mass fraction in the vessel; injection pressure
1100 bar, ambient density 22.8kg/m3 .
The mixing field may be characterized using probability density function of fuel mass fraction
in the vessel. For a homogeneous mixture the PDF shows a spike at the given fuel mass fraction
of the mixture. For a very inhomogeneous mixture the PDF shows a wide distribution
over the mass fraction of fuel. As seen in Figure 14, at later times, 2 ms to 5 ms, the fuel distribution
evolves with time to more homogeneous inside the vessel. This can be seen by the
growing peak at mass fraction value of 0.005 on the fuel mass fraction coordinate. The reason
for the high value of the PDF at fuel mass fraction of zero is the large air rich region in the
vessel. The highest value of mass fraction of fuel in the vessel is shown to decrease with time.
At early times, e.g. 0.5 ms, the fuel is still in the early mixing process; there is a wide interval
of different mass fraction values. A systematic parameter investigation for different injection
conditions including multiple injections of fuel is currently undertaken.
Direct numerical simulation of PPC
To improve the understanding of the structures and mechanisms of PPC ignition and reaction
front propagation, DNS is employed to simulate a H2 jet injected into hot air in a constant volume
vessel of 10x10x20 mm3 . The hot air has a temperature of 1000K and pressure of 30 bar.
The fuel is injected through a 1 mm diameter nozzle at 300K and 100 m/s. Figure 15 shows
the auto-ignition process characterized with the H radicals and fuel distribution at 5 consecutive
instants. The first frame from the left shows the start of ignition where the ignition site
is found at the low left side, slightly downstream of the nozzle. At this instant, the fuel jet is
not disturbed by the heat release; the upper half of the jet flow shows a wave shape due to
flow instabilities. After the onset of the ignition, the ignited zone grows quickly outwards to
both upstream and downstream directions. The fuel jet flow is disturbed by the gas expansion
due to heat release. The intensity of H radicals is highest at the propagation fronts indicating
more intense chemical reactions at the fronts; the ignition fronts propagates upwards at a
speed approximately of 400 m/s along the stoichiometric mixture surface surrounding the
fuel jet. Further DNS simulations are being undertaken for conditions with EGR and pressure/
temperature as well as fuels similar to the PPC experiments to be carried out in KC-FP. The
DNS data are currently being analyzed to find correlation between the onset of ignition and
the local flow and mixture properties, and the nature of reaction front propagation. In turn
the results are being used to validate LES models for simulation of flame and ignition under
PPC conditions.
17

Hadeel Solaka
PhD Student
Figure 15: Instantaneous H radicals (color contour, upper row), H2 (color contour, low row) and vorticity
isolines (white lines) in the symmetric plane of the constant volume combustion vessel. Results
are from DNS of H2/air mixture with injection velocity of 100 m/s at 300 K into hot air with 1000K.
1.5 PPC Fuels
Introduction
The traditional gasoline and diesel engine types have totally dominated the market for internal
combustion engines during the last century. The quantification and research on fuels
has during this time revolved around these engine types, creating indexes and understanding
that do not necessarily apply to other combustion principles in engines. Novel combustion
principles such as HCCI and PPC, principles that show potential for high efficiency and low
emissions operation, require new understanding on fuel properties.
Since most studies show that the oil reserves have started to decrease and that CO2 emissions
affect the climate in a negative way while at the same time the need for transportation is increasing,
the development of combustion engines faces three major challenges: Replacement
of traditional fuels- Low emissions operation – Low cost operation. Engine with high efficiency,
such as the PPC engine, are needed to meet these challenges. To fully exploit the potential
of the PPC engine, new understanding of the impact from fuel properties is a key issue.
Research
The Volvo research engine D5 has been converted to single cylinder operation, see Fig.16. It
is equipped with the new version of fuel system, piezoinjector, which replaced by a solenoid
injector. Replacing the new injector with an old version was due to mechanical problems that
occurred while running with gasoline as a fuel. The injector failed after reaching 800bars in
injection pressure. This failure was due to the fuel properties differences between diesel and
gasoline.
18

Figure 16 shows the research engine Volvo D5.
However, some experiments have been made with the piezoinjector in PPC-mode. These experiments
were run with gasoline (70 RON and 66 MON) and diesel MK1. By using fuels with
high octane number in diesel engine it is possible to achieve high efficiency and low emissions.
Previous research has shown that the heat release rate shape is improved by higher resistance
to auto-ignition which leads to higher efficiency.
With the new modification of the fuel system some experiments have been run with gasoline
69 octane number and diesel.
Results
The engine-out specific emissions of NOx and Soot are shown in Figs. 17 and 18, respectively.
The trends in these emissions from both experiments are quite similar: diesel gave higher
engine-out emissions than gasoline. Although not presented here, engine-out UHC and CO
emissions were also measured. The values for NOx and Soot were low but there is a penalty
from this that both UHC and CO were high. The trade off between Soot and NOx can be seen
in figs. 17 and 18.
180
160
140
120
NOx [ppm]
100
80
60
40
20
0
0 5 7,5
SOC [CAD]
19
Nox-Diesel @ 4IMEP[bar]
Nox-Diesel @ 7.2 IMEP[bar]
Nox-Diesel @10.5IMEP[bar]
Figure 17: Engine out emissions of NOx as function of load and start of combustion.

Anders Widd
PhD Student
Patrick Borgqvist
PhD Student
FSN [-]
2,1
2
1,9
1,8
1,7
1,6
1,5
1,4
1,3
1,2
1,1
1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
0 5
SOC [CAD]
7,5
20
Soot-Diesel @4IMEP[bar]
Soot-Diesel @7.2IMEP[bar]
Soot-Diesel @10.5IMEP[bar]
Soot-Diesel @13.2IMEP[bar]
Soot-Gasoline @4IMEP[bar]
Soot-Gasoline @7.2IMEP[bar]
Soot-Gasoline @10.5IMEP[bar]
Soot-Gasoline @13.2IMEP[bar]
Figure 18: Engine out emissions of Soot as function of load and start of combustion.
Future work
The coming research is focused on completing the current campaign which is comparing gasoline
fuel with different octane numbers and understanding how this is affecting the main
parameters in combustion (e.g. efficiency, Soot, NOx and maximum pressure rise rate). The
plan is to run 3 different engine speeds (1200, 1500 and 1800rpm) and make a load sweep (4,
6 and 8 bar) for each rpm and make another sweep of start of combustion (SOC) for each load
around (0, 5 and 10 CAD). Start of combustion (SOC) is defined as 1 % of heat release.
1.6 Combustion Control
Introduction
To the purpose of fuel efficiency and low emissions, the focus of this project is model-based
control of PPC. Physics-based models are favored due to the improved portability of the resulting
controllers as well as the added insight into the physical process. During the year, an
experimental study on mode switch between SI and HCCI has been completed. The attainable
high octane number gasoline partially premixed operation region is limited. Even with
advanced injection strategies and variable valve actuation, low load operating conditions may
be unattainable. One option is to apply combustion mode switching to and from spark ignited
combustion. Future and ongoing work involves modeling of PPC combustion to enable
optimization-based methods to be used for steady-state and transient operation.
Experimental Apparatus and Control System
The research engine hardware is a modified Volvo D5 passenger car size engine. The engine
is modified to run on only one of the five cylinders and is equipped with a fully flexible pneumatic
variable valve train system.
The valve timings are the most important parameters for mode switch control. The states
of the combustion and engine actuators are continuously updated at different rates by the
LabVIEW based engine control system. The engine control software is executed on a separate
target-PC, which is a dedicated real-time system, PXI-8110, running the LabVIEW real-time
operating system. The user interface is run on a separate Windows host computer. The host
PC communicates with the dedicated real-time PC over TCP/IP. The front panel of the control
system is shown in Figure 19.

Figure 19: LabVIEW engine control system front panel
Mode Switch Between SI and HCCI
During mode switches between SI and HCCI in early experiments, rather large variations in
IMEP were observed. The goal of this investigation was to reduce these variations and obtain
a smooth transition. It was discovered that a substantial amount of fuel was retained in
the intake port during SI operation, which produced large spikes in IMEP when the effective
compression ratio was changed to one suitable for HCCI operation. The switch was therefore
carried out by disabling the fuel injection during one cycle, and performing the change
in valve timings over 3 cycles. Closed-loop control was then activated to obtain the correct
steady-state combustion phasing and load after the switch. Two different control strategies
were investigated: PI and State Feedback control.
Figure 20 shows a mode switch sequence. The fuel injection is deactivated at cycle 0 while the
valve timing changes take effect. When closed-loop control was used, the PI-controllers were
activated at cycle 4 and the state feedback controllers at cycle 3.
Figure 20: Mode switch sequence showing the in-cylinder pressure, valve movements, and fuel injection
21

Two PI-controllers were implemented, one that governed IMEP using the fuel injection duration
as control signal, and one that governed the combustion phasing using the Negative Valve
Overlap (NVO). The controllers were tuned to produce optimized steady-state performance
around the nominal set points of combustion phasing of 6 degrees after top dead center and
an IMEP of 3.5 bar. Figure 21 shows the response following a mode switch around cycle 80.
There are noticeable oscillations in IMEP. These oscillations could likely be reduced by further
tuning of the controllers to this particular mode switch, but the PI approach is inherently limited
since there is no communication between the two controllers.
Figure 21: PI control following a mode switch showing the outputs IMEP and
CA50 (left axes) and the control signals fuel injection duration and NVO (right
axes).
To enable state feedback control, system identification was used to obtain a model with the
fuel injection duration and NVO as inputs and combustion phasing and IMEP as outputs. The
model was of fourth order and produced a VAF (Variance Accounted For) score of around
70-80 for both outputs in cross-validation tests. The controller was combined with a state
estimator and implemented in the LabVIEW-based engine control system. Figure 22 shows the
response following a mode switch around cycle 60. The response is a lot smoother than that
of the PI controllers.
Figure 22: State feedback control following a mode switch showing the outputs
IMEP and CA50 (left axes) and the control signals fuel injection duration
and NVO (right axes).
22

2. The Generic Diesel Project
Due to its relatively high efficiency, the diesel engine is an important power source for road
transport. Its importance can be expected to increase as the demands on fuel efficiency increase.
However, its exhaust emissions of oxides of nitrogen and particulates remain challenging.
One recent focus of the Generic Diesel (GenDies) project has been to clarify the mechanisms
behind trends in soot emissions during a wide sweep in exhaust gas recirculation (EGR). When
diluting the charge with EGR, soot emissions typically increase drastically. At a certain EGRlevel
they decrease again. These trends have been investigated by for the first time applying
time-resolved laser-induced incandescence (LII) in the cylinder of an optical heavy-duty
diesel engine.
Another focus has been sources of unburned hydrocarbons (UHC) in a low-temperature combustion
mode. The closing flank of the injector has been shown to cause drastically increased
air entrainment into the diesel jet. The resulting over-lean mixtures have been suspected to
contribute significantly to the UHC emissions. An experiment was devised to see if this overlean
mixture can be rendered combustible by a small post-injection. This experiment was
performed in collaboration with Dr. Mark Musculus at Sandia National Labs and showed that,
with the right injection strategy, this is indeed feasible.
2.1 Analysis of the Initial Soot Formation During an EGR Sweep
Introduction
During an Exhaust Gas Recirculation (EGR)-sweep, the engine out smoke level is typically
characterized by an initial increase with decreasing O mole fraction, followed by a drastic
2
decrease below a certain O level. In this investigation, a time-resolved analysis of the soot
2
distribution is made, in a reacting jet, during such a sweep in EGR.
Methodology
A Scania D12 heavy duty diesel engine, converted into an optically accessible single cylinder
engine of Bowditch design, was used in this investigation. A Multi-YAG laser system was
utilized to create time-resolved Laser Induced Incandescence (LII). The test matrix consisted
of a sweep in inlet O mole fraction between 9 and 21 %. The engine was operated at 6 bar
2
indicated mean effective pressure (IMEP). The crank angle of 50% completion of the heat
release and was kept constant at 9 CAD After Top Dead Center over the whole test matrix.
Results
As the O fraction was lowered from 21% to 9%, the engine out smoke level increased from
2
zero filtered smoke number (FSN) up to a peak of 2 FSN, occurring between 11 and 12% O , 2
from where it decreased down to zero again at 9% O . 2
Although it only represents a limited portion of the combustion chamber, the illuminated section
of the jet should capture the important trends during the early phases of soot formation.
As the portion of the laser sheet containing LII signal is related to the volume of the soot cloud
in the jet, the growth rate of the area is thus related to the soot forming rate. Figure 23 shows
the initial soot area growth rate as function of O fraction. The area growth rate is evaluated
2
as the slope of a linear curve-fit to the soot areas during the first 5 CAD with LII signal. The
soot area growth rate increases rapidly as the O fraction is decreased from 21% and peaks
2
at 13% O . As the O fraction is decreased further the soot area growth rate decreases again.
2 2
23
Clément Chartier
PhD Student
Ulf Aronsson
PhD Student
Johan Sjöholm
PhD Student
Joakim Rosell
PhD Student

Figure 23: The left graph shows soot area growth rate during the first 5 images with LII-signal from 10%
to 21% O 2 . The Images to the right show the raw signal and the derived soot area at -1 CAD ATDC for
14% O 2 .
Conclusions
The evolution of the in-cylinder soot distribution during an EGR sweep is consistent with and
helps explain the trends in engine-out smoke:
The initial growth rate of the soot area, in the plane of the laser sheet, increases when the O2 mole fraction decreases from 21% to 13% which is an indication of a greater net soot production
with decreasing O . It is reasonable to assume that the increased net soot production is
2
partially associated with reduced soot oxidation at low O fractions, although this cannot be
2
quantified from the present data.
Below 13% O , past the peak in smoke emissions the area growth decreases rapidly which
2
is explained by a decreased soot formation. As before, the oxidation is probably aggravated
under these conditions, but this is less important when a limited amount of soot is formed.
2.2 Post-Injection Effects on Near-Injector Over-Lean Mixtures
and UHC Emissions
Background
Low temperature combustion (LTC) is a concept aimed at reducing NOx and PM from diesel
engines by dilution of the charge with large amounts of cooled EGR. However, drawbacks in
terms of elevated UHC emissions are known for low load LTC conditions.
Previous studies have shown that over leaning of the jet after end of injection, due to enhanced
air entrainment, results in mixtures too lean to ignite in the near-injector region. This
behavior is especially seen at low loads when the ignition dwell, i.e. time between end of
injection and start of combustion, is large.
The potential was investigated of post-injections to locally increase the equivalence ratio and
render the mixtures ignitable, in order to reduce UHC emissions. Combined laser diagnostics
were used for indirect measurements of mixing. Combustion intermediates were used as indicators
of the local stoichiometry. Formaldehyde can be found in regions ranging from fuel
lean to fuel rich but it persists late in the cycle only in fuel lean regions. Furthermore, OH
concentrations are high in near-stoichiometric regions. Third, PAH is known as a soot precursor
and is found in overall fuel rich regions. Using combined OH and 355nm PLIF, the different
combustion intermediates can be imaged and give information about the local stoichiometry.
Formaldehyde and PAH can be extracted from spectral analysis of the 355-PLIF fluorescence
signal, since formaldehyde has a particular spectrum with seven distinct peaks between 385
and 445 nm.
24

Results
It was found that for a single injection, OH radicals are formed in the downstream regions
close to the bowl wall and stagnate in this location late in the cycle as shown in Figure 24.
Formaldehyde, i.e. lean regions, are found after EOI around the injector in the center of the
bowl as seen in Figure 25. No sign of fuel rich regions were observed for this case.
Figure 24: Evolution of the OH-radicals downstream position relatively to the injector
nozzle in the jet axis plane for the single injection compared to both investigated postinjection
strategies.
A post-injection strategy able to reduce measured exhaust UHC emissions was found to be
achievable, though very sensitive to the settings of the post-injection. A case with 20% decrease
in UHC emissions was found and repeatability tests showed good results. The postinjection
for this case was closely spaced after the actual end of main injection, by one CAD.
Rate of injection measurements showed that the momentum of the post injection is very low
compared to the main injection and that the fuel mass delivered in the post only is small (1.8
mg). Pressure wave dynamics in the injector body and common rail system are suspected to
cause this behavior since a one CAD shift in the start of post-injection, without changing the
energizing time, gave a similar momentum as the main injection.
The small post-injection caused a sudden appearance of OH radicals in the upstream part of
the jet by 10 CAD ATDC, see Figure 25. This observation indicates that second stage ignition
was made possible close to the nozzle by the post-injected fuel, which must have raised the
local equivalence ratio towards stoichiometry.
A second case of post-injection was investigated to show the sensitivity of the local enrichment
mechanism to changes in post injection strategy. The post-injection duration was kept
constant but its start was delayed by one CAD. Exhaust measurements showed no influence
of the post on UHC emissions for this case compared to the single injection. Furthermore, no
OH radicals were seen closer to the injector. Instead the same trend as for the single injection
was observed, see Figure 25.
25

Figure 25: Simultaneous OH (green) and 355 PLIF (red) images. The left frame is extracted from a sequence
with the single injection whereas the right one is from the small post injection strategy. The
timings are given relative to TDC and to the main EOI. The formaldehyde correlation bar indicates the
similitude of the 355 PLIF signal to a formaldehyde reference spectrum. The darkest colors in the correlation
bar indicate a low correlation whereas the brightest colors indicate that the LIF signal has a
high probability of being formaldehyde-LIF signal.
The fuel lean regions in the center of the bowl remained lean, correlating with the unchanged
UHC emissions. Rate of injection measurements showed that post-injected fuel mass was nine
times higher than the small post case and the momentum was similar to the main injection.
Conclusions
A comparison of the two post-injection strategies suggests that the momentum is crucial.
The post injection momentum should be low enough for the penetration to remain relatively
short. The post-injected fuel should thereby remain in the near-injector region to enrich the
over-mixed zones. Higher momentum in the post would carry the post-injected fuel too far
downstream. The discovery of the small post-injection strategy leading to exhaust UHC reduction
is the result of a trial and error process on the engine. This strategy can be seen as using
pressure dynamics in the fuel system to achieve such a small post injection. Injector dynamics
is not a controlled variable and the transfer of this particular injection strategy to another
engine might not be straightforward. However, the working principle of the local enrichment
by the post is valid and is the major novelty of this study.
2.3 Optical Diagnostics Development
New Ph.D. student in laser/optical diagnostics
During the fall the Ph.D. student Johan Sjöholm, who has been involved with the Gendies
program for almost five years, went on parental leave. At the same time a new Ph.D. student
was recruited. In late August Joakim Rosell joined the group. He has studied physics at Lund
University. After taking the master exam in Physics he studied pedagogics and thereafter he
has been working as a teacher both in Sweden and abroad. Joakim will be focusing on highspeed
diagnostics, mainly using the unique multi-YAG system, which is very well in line with
the needs of kcfp. Initially Joakim worked along with Johan Sjöholm in order to learn as much
as possible about the highly specialized equipment before Johan went on parental leave. During
the winter Joakim has focused on a feasibility study where the multi-YAG and an OPO-laser
are combined in order to target CO molecules. Joakim’s work includes both setting up the
laser hardware and performing test on CO in a controlled environment. If proven successful,
this approach will be used within in the GenDies program, for detection of partially oxidized
zones, in collaboration with visiting professor Paul Miles from Sandia National Labs.
26

Probing of CO molecules
Carbon monoxide, CO, is not only a major pollutant but can also be used as an indicator of
combustion efficiency, since incomplete oxidation of hydrocarbons result in increased concentration
of CO in the burnt gas region. It would thus be useful if this important species could be
monitored in combustion processes. In the ongoing feasibility study CO is probed by exciting
the molecule from its ground state to the excited state and then observing the fluorescence
that occurs when the molecule relaxes from the excited level to a lower. What is special about
laser induced fluorescence of CO is that it requires two-photon excitation in the UV (230.1
nm). This means that two photons must be absorbed for the excitation to take place. This is
in contrast to conventional laser induced fluorescence where only one photon is needed. The
reason for applying two-photon excitation in this case is that the single-photon transitions in
CO occur at wavelengths so short that the light would suffer from severe absorption when
transmitted in air. There are several issues with two-photon excitation. The most obvious are
the reduced signal strength and quadratic dependence on laser power, which means that high
power is required. A perhaps trivial but not less important task is to investigate how strong
CO-signals the new laser system can generate. Another important issue that needs careful
consideration is the interference from C -molecules. Spectrally CO and C can overlap, i.e. they
2 2
produce fluorescence of the same color. C can be formed naturally during combustion but it
2
can also be formed by photo decomposition of the fuel, i.e. introduced by the laser light. In
order to tell these two species apart it must be possible to distinguish CO-fluorescence from
C -fluorescence. There are strategies for this that are based on careful selection of the spec-
2
tral range where the detection is performed. The drawback of this approach is a significantly
reduced detectability, remember that the CO-signal is generally weak from the beginning and
further filtering worsens this. Quite recently another excitation scheme for CO, where laser
light at 217.5 nm is being employed (instead of 230 nm) was proposed. The amount of presented
work using this alternative scheme is very limited and Joakim Rosell is currently performing
comparisons of the two approaches. The potential advantage with the less applied 217.5 nm
excitation is a reduced interference from C . 2
Figure 26: Spectra from CO molecules after two-photon excitation.
27

Implications of applying LII in engine environments
Laser-Induced Incandescence (LII) has traditionally been considered a straightforward and reliable
optical diagnostic technique for in-cylinder soot measurements. As a result, it is nowadays
even possible to buy turn-key LII measurement systems. During recent years, however,
attention has been drawn to a number of unresolved challenges with LII. Many of these are
especially evident in regions with high soot concentrations typically found in combustion engines.
During the work of performing high-repetition rate measurements with LII in diesel
engines several specific challenges were identified. As a consequence, a substantial part of the
high-speed soot measurement campaign performed within the Gendies program was focused
on identifying and understanding the various issues associated with the application of LII in
engine environments in general and at high-speed in particular. This part of the work resulted
in a dedicated technical paper, on the application of high-speed LII in engines. This paper is
accepted for publication at SAE World Congress in 2011. All the identified issues might not
be possible to overcome but they should nevertheless be known and their potential impact
should be considered when interpreting the results.
In short, the LII signal depends on laser fluence. Ideally it is desired to have a plateau on the
fluence curve (LII-signal vs. laser fluence), i.e. a region where the LII signal is independent on
the laser fluence. This means that variations in laser energy do not influence the measured
soot amount. In practice the shape of the fluence curve is highly dependent on the laser beam
profile. A Gaussian profile will produce a LII-signal that continuously increases with laser fluence
and thus, does not show any plateau region. A perfect top-hat profile will introduce severe
sublimation and hence a weaker signal with increasing fluence. In Figure 27, the fluence
curves are shown for different beam profiles generated by altering the sheet forming optics.
Figure 27: The LII-signal versus laser fluence for different laser beam profiles. The
green curve represents a close to top-hat shaped profile that causes severe sublimation
of the soot particles. The blue curve represents a profile with more spatial
wings, i.e. closer to a Gaussian shape, which generates the desired plateau region
where the LII-signal is independent of the laser fluence.
28

In the initial feasibility study, high-speed LII measurements were made in a laminar ethylene/
air flame to test the characteristic features of high-speed LII in a well defined environment
before approaching the engine. Excessive influence of soot sublimation (damages of the soot
caused by the laser) was observed on the LII signals detected for later pulses in the pulse train
when running with pulse separations relevant for engine conditions, see Figure 28
Figure 28: Normalized LII signal from the second of two laser pulses sent through an atmospheric
flame as a function of pulse separation. The effect of soot sublimation is seen for
separations shorter than 20 ms.
Fortunately, corresponding data from the following in-cylinder measurements does not show
signs of the same behavior, which is believed to be due to high mixing and/or very fast soot
formation/oxidation in the measurement volume. This implies that time-resolved LII is a technique
applicable for qualitatively following the evolution of the soot distribution inside a reacting
diesel jet during a single combustion event.
29

Mehrzad Kaiadi
PhD Student
3. The Gas Engine Project
Introduction
Most heavy-duty engines are diesel operated. Severe emission regulations, high fuel prices,
high technology costs (e.g. catalysts, fuel injection systems) and unsustainably in supplying
fuel are enough reasons to convince engine developers to explore alternative
technologies or fuels. Using natural gas/biogas can be a very good alternative due to the
attractive fuel properties regarding emission reduction and engine operation. Heavy-duty
diesel engines can be easily converted for natural gas operation which is a very cost effective
process for producing gas engines. However, due to the high throttle losses and low
expansion ratio the overall engine efficiency is lower than for the corresponding diesel engines.
Moreover the lower density of natural gas results in lower maximum power level.
The existing project is the fourth phase of the natural gas engine project at Lund University.
The previous results show that the stoichiometric operation is a better choice than lean operation
since by using a 3-way catalyst the emissions level can be kept at very low levels and
differences in efficiency are not significant. Based on the previous results the engine operates
stoichiometric and the project focuses mostly on the problems associated with this type of
operation.
Extending the dilution limit of the engine and developing closed-loop control to operate the
engine at its dilution limit has been the main method to reduce throttle losses. New methods
to determine combustion stability during transients have been developed and used together
with model based control methods. New modifications are also performed on EGR and turbocharging
system of the engine to increase the overall efficiency and extend the maximum
load limit.
Objectives
The main objectives of the project during 2010 have been to identify and apply new hardware/strategies
to improve the overall engine efficiency and also extend the maximum load
level of the engine. A summary of the results achieved during 2010 are presented in this
report.
Experimental Results
Some modifications have been performed on the engine in order to improve the efficiency
and extend the maximum load limit. The main modifications were performed on the pistons,
the turbocharging system and the EGR system.
As already mentioned in last year’s report the major modifications on the pistons are
the shape and compression volume. The new pistons generate very high turbulence
and increase the compression ratio from 10.5 to 12. The results show roughly 40% reduction
in combustion duration and at least 2 percent units improvement in gross indicated
efficiency. The new combustion chambers are called “Quartette” in the figures.
The new piston modification results in some changes of the exhaust gas characteristics
and since the engine is equipped with a turbocharger with wastegate, the changes in exhaust
gas characteristics may have direct influence on the boost pressure. The absolute
boost pressure with Quartette pistons is lower which results in lower maximum BMEP.
30

Higher expansion ratio means that more heat is converted into mechanical work in the cylinder
and less energy in the form of exhaust gas enthalpy is available. According to the manufacturer
the exhaust gas temperature should be lower than 760oC. The lower exhaust gas
temperature obtained with higher compression ratio is beneficial in two ways. First, there is a
higher margin to the highest allowable exhaust gas temperature and second, there is potential
to extend the maximum load limit by replacing the turbocharger with a better matched unit.
A Variable Geometry Turbocharger (VGT) has the ability to change the turbine geometry in
order to obtain the desired boost pressure. VGT offers attractive properties such as high flexibility,
minimal amount of lag and wide operating range. VGT technology is extensively used in
diesel engines; however the use of VGT is very much ignored in gasoline engines due to their
relatively high exhaust temperatures. Ordinary VGT materials and designs cannot withstand
temperatures over 890°C. The exhaust gas temperature of gasoline engines could, however,
reach up to 1000°C, versus 650°C in diesel engines.
Normally natural gas engines use the same combustion technology as gasoline engines due
to similar fuel properties. In heavy-duty applications, since the engine speed does not exceed
2000 RPM, the exhaust gas temperature is not very high. After consulting with the R&D group
at Volvo a VGT was designed and mounted on the engine. The engine is operated at the same
engine speeds with WOT and by altering the geometry of the turbine housing the boost was
increased until either knock occurred or the pumping losses started to increase. To suppress
knock, EGR was added and the ignition timing was adjusted accordingly. Figure 29 shows the
boost pressure achieved by the VGT in comparison with the by-pass turbocharger with original
and Quartette pistons. The boost pressure was increased up to much higher levels with
VGT without sacrificing gas-exchange efficiency. The increase in boost pressure resulted in
increased maximum load as presented in Figure 30 compared to previous configurations. The
peak load increased by 18 percent from 16 to 19 bar BMEP.
Figure 29 Boost pressure achieved after replacing the turbocharger with a VGT
31

Figure 30 Maximum load achieved after replacing the turbocharger with a
VGT
Using a throttle always leads to pumping losses. Normally a throttle is used to control the desired
torque in the engines, but it is also possible to use a VGT instead of the throttle in a large
operating range to control the desired torque. This is possible due to the flexibility of the VGT
to adjust the inlet pressure by altering the geometry of the turbine housing. In this operation
region the throttle is kept fully open and the VGT is used to adjust the inlet pressure and finally
control the demanded torque. This means that the throttle will not be used in a large part of
the operating region (roughly 60% of the entire operating area of the engine) and no throttle
use means no throttle losses. The results have been validated in a large operating region and
showed that at least 2 percent units improvement in gas-exchange efficiency is gained. The
dynamics of VGT was also comparable to the throttle dynamics. An innovative driving strategy
with lowest possible throttle losses has been suggested. In summary the key features to
improve the natural gas engine performance are identified as: Right amount of EGR at different
operating regions, Right compression ratio, Variable Geometry Turbocharger (VGT), High
turbulence pistons, Long route EGR system and model-based control.
Planned Activities
Mehrzad Kaiadi will defend his doctoral thesis 2011-02-11. After that the project will focus on
dual fuel operation using direct injection of Diesel fuel for ignition.
32

KCFP
Kompetenscentrum Förbränningsprocesser
Centre of Competence Combustion Processes
Faculty of Engineering, LTH
P.O. Box 118
SE-221 00 Lund
Sweden