Mitsubishi Heavy Industries Technical Review Vol. 47 No. 4 (December 2010)13Direct High-speed Exhaust Gas Measurement System
Using Semiconductor Laser- A Useful Tool for Developing Energy-efficient Engines and Urea SCR Catalysts -Tr a n s p o r ta t i o n S y s t e m s & A d v a n c e d
Te c h n o l o g y D i v i s i o n
Advanced Mechanical Systems
D e pa r t m e n t

Although the development of electric vehicles is being promoted to achieve a low-carbon
society, the mainstream of motive power for the near future will be internal combustion engines.
A system capable of making measurements within 1 ms is required to capture the phenomenathat occur during the engine combustion cycle, so that the transient combustion in internal
combustion engines can be analyzed in depth to further improve fuel efficiency and reduce
emissions. While emission regulations are becoming increasingly stringent, EURO VI, thenext-generation standard in Europe, requires a high-accuracy measurement system to measureammonia (NH3), which will be subject to control.

|1. Features of SUPPLEA and TDLAS
1.1Super-prompt Laser Exhaust Gas Analyzer (SUPPLEA)

The super-prompt laser exhaust gas analyzer (SUPPLEA) can measure exhaust gas
temperatures and multicomponent (H2O, CO, CO2 and CH4) gas concentrations with an ultrafast
response in 1 ms. The following are some possible applications.
(1) Because of its 1-ms ultrahigh-speed response direct measurement, SUPPLEA can visualizetransient phenomena during an engine combustion cycle and identify phenomena neverbefore captured, such as fuel-rich/lean combustion, misfire detection and variation between
cylinders. Therefore, the system can be applied to engine development, including hardware
and software.
(2) With the combination of a fast response flowmeter and a total hydrocarbon (THC) analyzer,
an ultrafast response fuelometer (on ms order) is expected to be put into operation.
(3) SUPPLEA is a portable system that can be mounted on an actual vehicle for on-vehicle
measurement. Using the same measuring device in test bench experiments and field tests, it
is possible to eliminate instrument error between the devices used at different testing stages
and considerably shorten the engine development period.
(4) Gas temperature measurement unaffected by the radiation heat from the piping is possible
because the temperature is measured by thermal analysis based on the H2O absorption
spectrum.

1.2

Tunable Diode Laser Absorption Spectroscopy (TDLAS)

Tunable diode laser absorption spectroscopy (TDLAS) is capable of high-speed response
measurement (≤100 ms) of NH3 on the order of ppm. The following are some sample applications.
(1) TDLAS can accurately measure NH3, which will be controlled under the EURO VI
regulations (regulated value: 10 ppm).
(2) The system can measure the NH3 distribution in a catalyst system based on simultaneous
measurements at two points. This shortens the development period of NOx reduction
after-treatment systems (urea SCR catalyst) and enables development aiming at reducing theamount of catalyst (cost reduction).

Mitsubishi Heavy Industries Technical Review Vol. 47 No. 4 (December 2010)
14(3) Being capable of a fast response (100 ms), the system enables the visualization of momentaryammonia slip, which has been difficult with the conventional measurement system, Fouriertransform infrared spectroscopy (FTIR).

|2. Specifications of SUPPLEA and TDLAS
The specifications of the systems are summarized in Table 1.
Table 1

System specifications

SUPPLEA
Measurement
principles
Type of gas
measured, etc.

Direct measurement

TDLAS
Sampling-type measurement

Semiconductor laser absorption
spectroscopy

Semiconductor laser absorption spectroscopy

H2O, CO, CO2, CH4; Temperature

NH3

Measurement
range

Temperature: 30 - 800 (°C)
H2O, CO2: 0 - 20 (vol%)CO: 0 - 10 (vol%)CH4: 0 - 1,000 (ppm)

NH3: 0 - 1,000 (ppm)

Response time

1 msDimensions(W × H × D)(mm)

435 W × 385 H × 365 D (mountableon a vehicle)

Weight35 kg

Detection limit(2σ)

CO, CO2, CH4: ±2 (%/FS)@ 25°C & 0.1 MPa abs.
H2O: ±2 (%/FS)@ 150°C & 0.1 MPa abs.
Temperature: ±10 (°C)
@ 150°C & 0.1 MPa abs.

200 ms or less(at a sampling flow rate
= 12 L/min)
540 W × 1,200 H × 800 D(measurement panel)
540 W × 1,200 H × 800 D
750 W × 877 H × 300 D(sampling rack)
120 kg (measurement panel)
85 kg
80 kg (sampling rack)
100 ms5 ppm@ 300°C & 0.1 MPa abs.

2 ppm
@ 300°C & 0.1 MPa abs.

|3. Examples of measurements
3.1

SUPPLEA

3.1.1

Visualization of Transient Phenomena
With the conventional sampling-type measurements, it is difficult to increase speed dueto the time required for pre-treatment and supplying the sampling gas to the analyzer. As aresult, sampling-type measurements could not have precisely captured the transient phenomena
occurring when the concentration changes. Examples of transient phenomena visualized using
SUPPLEA are as follows:(1) Engine start
As shown in Figure 1, the system precisely captured the appearance of unburnt carbon(CH4) and CO momentarily because of incomplete combustion during cold startup.
(2) Fuel cut
As shown in Figure 2, the system precisely captured the appearance of CO and CH4transiently during fuel cut. This contributes to optimizing control by the electronic control
unit (ECU).
3.1.2 Applications in Misfire Detection
Misfire detection requires responsiveness that can meet the speed of the engine
combustion cycle. When a four-cylinder engine is operated at 6,000 rpm, the required cycle tomonitor each cylinder is the following equation.
6,000 rpm × (1 combustion stroke/2 rotations) × 4 cylinders ÷ 60 sec = 200 Hz (5 ms)
Therefore, SUPPLEA can be applied to misfire detection because it has a responsivenessof 1 ms, which enables five-point sampling during one combustion cycle. The graph on the leftof Figure 3 shows the SUPPLEA measurement waveform that was obtained when asingle-cylinder engine was operated at 3,600 rpm. The results of fast Fourier transform (FFT)
analysis of engine revolution and the gas temperature shown on the right side of Figure 3 bothcoincide at 30 Hz, indicating that the system precisely visualized the variation in gas
temperature during the engine combustion cycle.

Mitsubishi Heavy Industries Technical Review Vol. 47 No. 4 (December 2010)
15Figure 1 Transient phenomena during
engine start

Figure 2 Transient phenomena during
fuel cut

Figure 3 Gas temperature measurement and FFT results

3.2TDLASThe NH3 concentration was measured by TDLAS (sampling-type and direct measurements),
while the amount of NH3 supplied was increased in a stepwise manner at 2-sec intervals. The
maximum amount of NH3 supplied was approximately 500 ppm.
As shown in Figure 4, the response of the sampling-type measurement was approximately
200 ms, while that of the direct measurement was about 100 ms. These results matched the amountof NH3 supplied.

Figure 4

Measurement results