Transition Region Exhaust
Gas Measurement Using
High-Speed Response Laser
Equipment
KENJI MUTA*1

MASAZUMI TANOURA*1

AKIO KONDOU*1

ATSUSHI TAKITA*2

SHINICHIROU ASAMI*3

EIJI KATO*3

Mitsubishi Heavy Industries, Ltd. (MHI), has developed a compact laser exhaust gas measurement device that can directly
measure the gas temperature and concentration at high speed in engine pipes for furnace monitoring applications such as boilers
and refuse incinerators. In this report, we describe the equipment and show, using case studies, how new insights have been provided
by using it for exhaust gas measurement during transient operation of test bench engines or vehicles, in situations where data are
difﬁcult to obtain with conventional equipment. We also show the effectiveness of this equipment in the development of engine andexhaust gas treatment systems.

1. Introduction

2. Laser engine exhaust gas measurement equipment

M H I has been i nvolved i n developi ng laser- based
measurement technolog ies for gas concent rat ion a ndtemperature in furnaces for applications such as boilers andrefuse incinerators.1,2 As this measurement technology isa noncontact method, real-time measurement is possible,
avoiding the delays inherent in measurements based on gas
sampling. We are currently adapting this technology for use inengine exhaust measurements in automobile applications. This
has required two new advances: improvement of the responsetime to the millisecond range, and development of a sensor that
could be directly attached to the exhaust pipe of an automobile.
In this report, we describe our high-speed responseengine exhaust gas measurement equipment, which includes
these two developments. We also show how this equipment
can be used effectively in engine development by obtaining
information not easily obtained by conventional equipment in
the case of transient engine conditions in which the engine
load changes rapidly.

The current laser exhaust gas measurement equipment
is based on laser absorption spectroscopy technolog y,which derives the gas concentration and temperaturefrom the optical absorption at a specific wavelength. The
actual measurement of concentration and temperature in
the exhaust gas is obtained by the analysis of laser lightfalling on the measurement sensor (measurement cell) after
passing through the exhaust gas. The sensor is attacheddirectly to the exhaust pipe with optical fiber as shown in
Fig. 1, and the analysis takes place in the main equipment
component.
MHI has commercialized both high-speed and highaccuracy measurement equipment using different control
and analysis methodologies with the same laser absorption
spectroscopy principle.
2.1 Equipment overview(1) High-speed response laser exhaust gas measurement
equipment

Exhaust pipe being measured
Engine exhaust gas

Optical fiber
Main equipment
component(Laser)<Measurement cell> Light receptor

Electric cable(Light reception signal)

Fig. 1 Laser exhaust gas measurement equipment
Typical equipment system used for measurement of gas in a pipe.
*1 Advanced Technology Research Center, Technical Headquarters*2 Yokohama Research & Development Center, Technical Headquarters*3 Kobe Shipyard & Machinery Works
11

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)

PC fordisplay purposes
Input/output
terminal box
LAN cable

PC for analysis

LAN cable(Light reception signal)(Light reception signal)

Control/
analysiscomponent

Measurement
cell
Optical fiber

Optical fiberconnector

Optical fiber(10 m and over 10 m)
Exhaust gas
Exhaustgas

Fig. 2 Super prompt laser exhaust gas analyzer (SUPPLEA)
T hi s h a s a ve r y fa s t m e a s u re m e nt tim e of 1 m s, a n d c a nsimultaneously measure the gas temperature and concentrations of
H 2 O, CO, CO2 , CH4 , and O2.

Measurement
cell

Opticalfiber
connector

Opticalunit

Fig. 3 High-accuracy/super prompt laser exhaust gas analyzer(TDLAS)This device can measure the par ts-per-million constituent
concentrations of NOx and NH3 at two points simultaneously with a
response time of 100 ms or less.

Figure 2 shows a schematic of the Super Prompt
Laser Exhaust gas Analyzer (SUPPLEA). This highspeed equipment consists of the measurement cellattached directly to the exhaust pipe, the main equipment
component, and a personal computer (PC) for analysis
and display. It simultaneously measures the exhaustgas temperat ure and the concent rat ions of the gas
components (e.g., H 2 O, CO, CO 2 , CH 4 , and O 2 ) with atime resolution of 1 ms. This equipment is used mainly insituations where the quantity of solid particulates is low,such as in engine exhaust gas.
(2) High-speed response/high accuracy laser exhaust gas
measurement equipment
Figure 3 shows a schematic of the Tunable Diode Laser
Absorption Spectroscopy (TDLAS) device that can perform
high-speed measurements of minor gas components
such as ammonia (NH 3 ) or nitrogen oxide (NOx) at theparts-per-million level. This equipment also consists of ameasurement cell attached directly to the exhaust pipe,

the main equipment component, and a PC for analysis anddisplay, and has a measurement time of 100 ms or less.
This equipment is used mainly for the measurementof diesel engine exhaust gas because it is affected very
little by solid particulates. It is also possible to measure
the gas concentrations at two points such as before andafter the exhaust emission control catalyst, with one set of
equipment.
Table 1 summarizes the features of both types ofequipment.
2.2 Measurement cell
While there are various configurations corresponding
to different pipe sizes, they all use the two typical types ofmeasurement cell.
(1) Multipath cellThis cell can be installed directly into an existing ﬂange
because the sensor is very thin, as shown in Fig. 4.3 It hasa pair of mirrors conﬁgured to achieve multiple reﬂections

Table 1 General speciﬁcations for MHI’s laser exhaust gas measurement equipment
Product name

1.SUPPLEA*1

2.TDLAS*2

Features• Super-fast responsiveness (1 ms)• Simultaneous measurement of multi-constituent
concentrations (% level) and temperature• Measurement at 1 point• High-speed responsiveness (100 ms)• High-accuracy measurement of single constituent
concentration (ppm level)• Simultaneous measurement at 2 points

Application• Gasoline engine exhaust gas• Exhaust gas after diesel particle filter (environment
without solid particulates)• Diesel engine exhaust gas• Gasoline engine exhaust gas (not affected by solid
particulates)

Details• Measures H2O, CO, CO2, CH4, and O2 simultaneously• Measurement range of gas temperature: 150–800°C• Measures one of the following at a time: NH3, NO, NO2, N2O,
or others

Measurement
principle

Laser absorption spectroscopy(high-speed wavelength scan and change detection)*1: SUPer Prompt Laser Exhaust gas Analyzer

Laser absorption spectroscopy(Wavelength modulation method)*2: Tunable Diode Laser Absorption Spectroscopy

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)12

purging system. This cell permits maintenance-freemeasurement by eliminating the optical parts that are
in direct contact with the exhaust gas, and by injecting
purging gas to prevent the accumulation of contaminantson the window. However, the cell is larger and thicker
than the multiple-reﬂection type, and some modiﬁcationof the pipes may be required for some installations. This
type of sensor is used mainly for the measurement ofdiesel engine exhaust gas.
The cell shown in Fig. 5 (a) is for a small-diameter
pipe of approximately 50 mm or less, while that shown in
Fig. 5 (b) is for a larger-diameter pipe of 115 mm or more.

Optical mirror(reflectance ≥ 99 %)Laser
Optical fiberGas flowLight
receptor

3. Case study of automobile exhaust gas
measurement
Fig. 4 Multi-path cell 3
As the sensor is very thin, it can be attached directly to the ﬂange ofan existing pipe.

Here we discuss a case study of exhaust gas measurement
using this equipment with an automobile under transient
operating conditions, such as those in which the loadchanges rapidly. Usually, exhaust gas measurement undersuch conditions is difﬁcult with conventional methods. We
also describe the effectiveness of this equipment in thedevelopment of engines and vehicles.

so that laser light is transmitted to every part of the pipe
cross section. This has the following advantages: theaverage cross-section value can be obtained without
being affected by the distribution of the concentration ortemperature in the pipe, and the optical path length canbe increased to improve the measurement sensitivity.
However, contamination of the mirrors is a problem
since the exhaust gas and the mirrors are in directcontact with each other. Therefore, this sensor is suitable
mainly for the measurement of gasoline engine exhaust,
or diesel engine exhaust downstream from the diesel
particle ﬁlter, where few solid particulates exist.
(2) Single-path cell with air purge system
F ig u re 5 shows a si ngle - pat h cel l w it h a n a i r

3.1 Example of measurement results from passenger
car chassis dynamo test
T he chassis dynamo test of a passenger car can beeasily performed with conventional sampling instruments.
However, because the responsiveness of convent ional
instruments is as slow as several seconds and the gas
sampling equipment must be near the engine, measurement
at the tail-pipe is often used, even if there is a delay from theactual engine behavior. This makes it difficult to evaluate
the engine behavior accurately under transient conditions.
On the other hand, the laser exhaust gas measurement

N2

N2

Light receiving system

500 mm or less
Optical fiber

N2

Light receptor
Exhaust gas

Thermocouple

Light emitter

Thermocouple for gas temperature(a) Cell for small diameter pipeN

Measurement cellLight receptor2

erThermocoupleLasLight emitterrbeLight receiving systemfi
Optical N2
alictsystemp
O(b) Cell for large diameter pipe

Laser
Exhaust gas

Fig. 5 Single path cell with air purging system
Even in the presence of particulates, maintenance-free measurement is possible for (a) small diameter pipes and (b) large diameter pipes.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)13

Fuel flow reduction

16
12

CO2

8
4
0
600

Instantaneous change ofconcentration/temperature

200

CO

160
120

500
400
300
200

Gas
temperature

80
40

Vehicle speed
60

80
100
120
Measurement time (s)Temperature fluctuationand concentration fluctuationfor each combustion cycle
Vehicle speed(km/h)

Gas
Gas
temperature (%) concentration (%)

Gear change
20

0

140

Fig. 6 Example of rapid exhaust gas measurement during mode driving test
Combustion fluctuation for each cycle can be measured, and the effect of instantaneous transientphenomena such as gear changes and fuel ﬂow reduction can be observed.

concentration in the intake gas on the vertical axis as afunction of the crank angle. Notes (1)−(5) in the ﬁgure show
the degree of overlap of the inlet and outlet valves; as thenumerical value increases, the amount of overlap increases.
We observed that there is very little CO 2 in the intake gas
under the condition of (1) without overlap, and that the CO2
concentration increases rapidly, and its peak appears earlier,as the overlap increases.
Since this overlap flow can now be measured in real time,
as opposed to with a numerical simulation only, it is possible tomeasure/control the optimal overlap amount based on actual
measurement results.

equipment developed by MHI has a very short measurement
time, and the measurement cell can be easily installed at any
arbitrary location along the tailpipe without any modiﬁcation
to the pipe. This makes it easy to capture information in
the transient region of engine operation during the chassis
dynamo test.
F ig u re 6 shows a n ex a mple of l a s er ex haust g a s
measurement at the exhaust manifold outlet for 10 –15
driving modes on the chassis dynamo. Transient phenomena
relating to engine control are clearly recorded, including the
instantaneous changes of gas concentration and temperaturecorresponding to slight changes of throttle setting due togear changes or variations in fuel flow. At first glance, itwould seem that the CO2 concentration and gas temperaturesfluctuate widely. However detailed analysis reveals thatthese f luctuations are directly related to the combustion
cycle of each piston.
Thus, high-speed transient phenomena and the ﬂuctuationof each combustion cycle can be easily measured with thisequipment even with the chassis dynamo test. This cancontribute to faster development or upgrading of vehicles sothey run more cleanly with better fuel efﬁciency.

Upper dead center
Valve overlap
Outlet valve closed
Inlet valve opened(variable)

Inlet valve closed(variable)
CO2 concentration (%)

3.2 Understanding the amount of gas overlap ﬂow on
an engine test bench
One type of current engine control stabilizes combustion
by increasing the overlap of the inlet and outlet valves in highload regions and returning some portion of the exhaust gas
to the intake in the form of overlap ﬂow.
The objective of the example shown here is to verif ywhether the amount of exhaust gas that enters the intake (i.e.,
the amount of overlap ﬂow) can be determined by high-speed
measurement of the CO 2 concentration using SUPPLEA in
the air intake between the intake manifold and the intake
port during the bench test of a gasoline engine.
Figure 73 illustrates the measurement results. Thisgraph shows crank angles on the horizontal axis and CO 2

– 60

(5)
(4)
(3)

(5) (4)(3)(2)(1)

Outlet valve opened
Bottom dead center• Inlet valve (variable phase)• Outlet valve (fixed)

(2)
(1)

0

60 120 180 240 300 360 420 480 540 600 660
Crank angle (°)

Fig. 7 Measurement of the overlap ﬂow rate as a function of
overlap amount of inlet valve/outlet valve 3
High-level engine combustion control is simple because the overlap
ﬂow rate of exhaust gas to the intake side can be measured in realtime.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)14

This example shows that our equipment makes it possible toadjust advanced engine combustion controls simply and easily.

for the evaluation/control of the deNOx system above, theMHI equipment can easily evaluate and control the system.
This will help accelerate the development of more advanced
deNOx systems.

3.3 NH3 concentration measurement in a diesel
passenger car
Urea selective catalytic reduction systems help improvethe control of diesel emissions. In this type of system, it isimportant to control the optimal injection volume of NH 3 asa function of the amount of NOx generated. NH 3 also plays
an important role in the de-nitrification (deNOx) of NOx
storage catalyst.
S i nc e N H 3 is a s ubst a nc e w it h st ron g abs or p t i ve
properties, accurate measurement of its concentration is
difﬁcult using gas sampling. This is particularly so in a casein which the concentration changes rapidly (transient regionof concentration change), and the response delay with thesampling method makes detecting changes very difﬁcult.
Therefore, we describe a case study in which TDL AS
is used to measure the concentration of NH 3 in diesel
exhaust gas. We recorded the quantitative results andresponsiveness of measuring the NH 3 concentration in
the exhaust gas at the tail pipe of a diesel passenger car
using TDLAS with a single path-cell and air purge system,
and compared these to the results obtained using the gas
sampling method.
During the test, exhaust gas containing NH 3 of a certain
concent rat ion was f irst measured to conf ir m that themeasurement values using both methods were the same.
After that, the measurement results were compared whiledriving the car under conditions in which the amount of NH3
generated changed in sharp spikes (i.e., rich spike condition).
Figure 8 shows the measurement example with the
NH 3 concentration (upper graph) and the signal for NH 3
production (lower graph) as a function of time; the NH 3
is produced during the spike signal. This equipment canmeasure the change of NH 3 concentration synchronizedwith the spike signal while conventional instruments hardly
register the change at all.
Thus, while conventional instruments lack responsiveness

MH I has developed compact laser ex haust gas
measurement equipment that can measure engine exhaustgas at high-speed.
(1) High-speed response laser exhaust gas measurement
equipment (SUPPLEA)• Simultaneous measurement can be achieved for gas
temperature and concentrations of H 2 O, CO, CO2 , CH4 ,O2 with a response speed of 1 ms.
• One set of equipment measures one location.
(2) High-accuracy laser exhaust gas measurement equipment(TDLAS)• Concentration can be measured with high-accuracy on
a parts-per-million level with a responsiveness of 100
ms or less.
• One set of equipment can simultaneously measure twopoints, such as before and after the catalyst.
M H I i nt ends t o a s sist c ust omer s i n t hei r produc tdevelopment by prov iding this equipment in order tohelp them understand various phenomena that cannot be
investigated conventionally. This includes the following:(1) High-speed phenomena that are other wise dif f icult
to observe, such as the change of concentration andtemperature for each cycle of the engine combustion
process.
(2) Changes of NH3 concentration that are difﬁcult to detectby sampling measurement; this is very important in thedevelopment of future exhaust gas treatment systems.

References
1. Muta et al, Proceedings of the T hirt y-fourth Symposium on
Combustion (1996) p.551
2. Muta et al, Proceedings of the Thirty-seventh Symposium on
Combustion (1999) p.465
3. Yamakage et al., Transactions of Society of Automotive Engineersof Japan, Vol.39 No.2 March 2008 p.123: Laser NH3 Analyzer: Conventional measurement value (FTIR)

NH3
concentration
Signal forNH3 production
operation

4. Conclusion

0
ON

5

10

15

20

25
30
35
Measurement
time (s)40

45

Kenji Muta

Masazumi Tanoura

Akio Kondou

Atushi Takita

Shinichirou Asami

Eiji KatoOFF

FTIR: Fourier transform infrared spectroscopy

Fig. 8 Measuring ammonia production during a rich spike
More advanced deNOx systems can be designed and controlledusing laser measurement equipment to measure prompt NH 3change.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)15