This document describes the development of a low-cost adjustable gaseous exhaust analyzer for runtime characterization of vehicle emissions. The analyzer uses a telescopic tube arrangement to passively control exhaust temperature for different sensor needs. It can monitor CO, NOx, CO2, and humidity concentrations in real-time. The analyzer was validated against commercial instruments, showing results within 20% error. Future work will incorporate flow sensors and monitor additional gases to allow for a more complete emissions analysis.

1. International Conference
on
Automotive Technology
Development of a Low-cost Adjustable
Gaseous Exhaust Analyzer for Runtime
Characterization
Pradip Gatkinea*
, Rachit Aggarwala
, Pushkar Limayea
, Nimish Mehtaa
a
Dept of Mechanical Engineering, IIT Bombay, Mumbai, India
*Corresponding Author. Tel:+91 9820685649, E-mail:pradip_gatkine@iitb.ac.in
Manuscript received July XX, 2013; revised August XX, 20XX
Abstract
It is important to characterize the IC engine for emissions of an automobile and thus provide a runtime feedback to
vehicle design engineers especially in academic domain to improve the performance towards a greener vehicle. The
instrument described in this paper is a simple equipment with a unique extensible telescopic tube arrangement for adjustable
passive temperature reduction and thus providing automatic temperature gradient as per the need of different sensors
deployed. The instrument currently has capability to monitor and log volumetric concentrations of CO, NOx and CO2 as well
as humidity measurement. A temperature sensor has been employed with each gas sensor for temperature correction.
Readings from all the sensors are processed in real time on the onboard microcontroller and are also relayed over a wireless
channel as per the need. The instrument can be fitted to exhaust pipe using minimalistic support structure and thus used for
run-time monitoring of the exhaust. A validation of the instrument has been done in no load condition on BAJA mini vehicle
of IIT Bombay against 2 industrial grade exhaust analyzers (by NETEL, India) and results matched closely
Keywords: CO, emissions, humidity, NOx, telescopic tube
1. Introduction
It is important to characterize the IC engine for emissions of an automobile and thus provide a set of
parameters for vehicle drivetrain tuning to improve the performance towards a greener vehicle. For carburetor
based IC engines, it provides the optimum air-fuel ratio. This necessitates a runtime monitoring which will enable
designers to track emissions of vehicle in running condition on a controlled path, traversing through a controlled
set of loads and accelerations. This also helps in selecting optimum catalytic converters. The commercially
available test instruments do an extensive active treatment of the exhaust (to remove moisture and to control
temperature). So they are huge, importable and expensive and also not useful for run-time feedback. Commercial
instruments pose costs of the order of 30,000 USD [1], making it completely inaccessible for vehicle
developments in academic or research environment.
CO, NOx, and relative humidity (RH) provide the most significant information towards engine tuning. The
design objective is to minimize CO and NOx emissions. CO concentrations provide a way to tune fuel pressure at
the injector. NOx concentrations provide a handle on engine cooling design [2]. Relative humidity provides a
measurement of degree of combustion at a given temperature. To accurately determine the concentrations, it is
important to measure temperature and flow rate as well.
A custom made exhaust analyzer has been designed to cater to the above requirements in context to design of
an All-Terrain Vehicle. The sensors used in the design of this analyzer are off-the –shelf and have been
calibrated. A novel concept of achieving a temperature distribution is implemented in the form of an adjustable
telescopic tube arrangement. A fast wireless long-distance data acquisition system is designed and implemented

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in order to make continuous measurements of the vehicle during a test run. The data analysis is done in base
station which gives a timed log of concentrations.
The paper outline is as follows. Section II describes System Overview. Sensor response, concentration
extraction and calibration procedure are discussed in Section II. Test results are elaborated in Section IV and
conclusions in Section V.
2. System Overview
2.1. The Adjustable Telescopic Tube Arrangement
The main objective of the design of telescopic tube is to serve the purpose of mount for the sensors and
onboard electronics as well as to facilitate a variable temperature distribution that can be attained based on the
specific application of the analyzer and the specific choice of sensors. It consists of a primary and a secondary
tube. Primary tube mainly reduces the temperature of the exhaust below 1000C, thus eliminating possibility of
superheated steam and increases the pressure close to atmospheric pressure. It is 30mm in diameter and 40cm in
length. It is flattened at the bottom to facilitate mounting on a telescopic channel. It is made up of a foam-based
material.
The secondary tube is 52mm in diameter and 400mm in length and is made up of foam-based material. The
sensors and onboard electronics are mounted towards the end of secondary tube between 300-400mm range. A
temperature sensor is mounted along with each exhaust sensor to measure temperature of gas at that point.
The cavity between primary and secondary tubing is filled with a dense cotton plug when the length
adjustment is finished. The length is adjusted such that the temperature of the exhaust gas in the sensor region is
between 40º-50ºC so that appropriate sensitivity of the sensors is ensured. The bottom part of the secondary tube
is flattened at the bottom for mounting it on the telescopic channel. The overall weight of the assembly is 1.5kg.
Fig. 1. The designed telescopic tube model with dimensions
2.2. Sensor Electronics
1) CO Analyzer:
A Tin Oxide (SnO2) based CO sensor MQ7, manufactured by Henan Hanwei Electronics is used. Sensitive
material of MQ-7 gas sensor is SnO2, which has lower conductivity in clean air and higher when the CO
concentration is high. It makes detection by method of cycle of high and low temperature, and detects CO when it
is at low temperature part of cycle (heated by 1.5V for 90 seconds). At high temperature part of cycle (heated by
5.0V for 60 seconds), it cleans the other gases adsorbed under low temperature. It is important to achieve the
heating cycle accurately. This is achieved through the timer in onboard ATmega2560 microcontroller.

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Fig. 2. The schematic of the circuit for MQ-7 Sensor[3]
2) NOx Analyzer:
A Tin Oxide (SnO2) based NOx sensor MQ 135 manufactured by Henan Hanwei Electronics is used. The
heater circuit provides necessary work conditions for work of sensitive components. This sensor is sensitive to
many gases like NH3, CO2, CO, Benzene, ethyl alcohol and NOx. But in case of exhaust analysis, CO2 and CO
are present in large amounts and hence, make the sensor insensitive to them. Also the amounts of NH3, alcohol
and benzene are close to zero. Thus the sensor is most sensitive to NOx during exhaust analysis.
Fig. 3. The schematic of the circuit for MQ-135 Sensor[4]
3) Relative Humidity Analyzer:
HSM 20G humidity sensor module is used for this purpose. It provides a linear output proportional to the
relative humidity value. Temperature variation changes the slope which is tabulated in the datasheet [5].
Fig. 4. The HSM-20G RH Module (Front and Back)
2.3. Data Acquisition and Communication
The objective of the exhaust analyzer development is to establish a low-cost procedure to tune vehicle
drivetrain parameters towards a target emission level. Hence it is important to log the drivetrain prameters along
with emission parameters in real time. An ATmega2560 microcontroller based custom data acquisition system
was developed for the All-Terrain Vehicle , Prithvi 3.0, for measuring engine RPM, wheel RPM, longitudinal
and lateral acceleration, exhaust gases concentration and location using GPS. All the content monitored by the
system was wirelessly relayed to a base station using Xbee Pro 802.15.4 radio. Except for the GPS, the above
parameters were sampled at the rate of 20Hz (GPS at 5Hz rate) with each data entry of 40 bytes. It was also
equipped with a 2GB SD card for storing all the entries to avoid data loss in case of wireless communication
failure.
3. Calibration Setup
The CO and NOx analyzer were calibrated using a single test setup. It consists of a standard chamber in
which a standard incense is allowed to burn [6]. The chamber is also attached with a fan to avoid stagnation, to
Vc: 5.0V±0.1V
VH（High）: 5.0V±0.1
VH(Low）: 1.5V±0.1V
VRL = Output voltage

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maintain the flow of air and to ensure mixing of the effluents. The analyzer tube is mounted on the outlet and
also serves the purpose of air and exhaust vent. The chamber is cubical with side 1m. The calibration test is
carried out for 1 hour to check for the extended stability of the analyzer setup.
Fig. 5. The schematic of the data acquisition and communication setup developed.
Fig. 6. The Calibration test setup for CO and NOx Analyzers
Fig. 7. The calibration response of CO analyzer. First 4000 time steps are for ambient air (5 ppm) and next 4000 time steps are
for the calibrator (1450ppm).
The response obtained by the test for CO and NOx are shown in Fig. 7 and 8 respectively. The expression for
CO ppm is given by [3]:
-1.4 + log (Rs / R0) = -0.7 × log(ppm) (1)
where, R0 is value of filament resistance at 100ppm. Its variation with temperature and humidity is provided in
MQ-7 [3]. Rs can be calculated from output voltage VRL:
Rs = (Vc/VRL - 1) × RL (2)

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where Vc and RL are shown in Fig 2. VRL is the minimum value in discharge (descending) cycle in Fig.6. Value of
R0 for this test setup (RL = 10kTemperature = 35ºC and RH = 30%) was found to be 13.4 k.
Similar calibration is followed for NOx analyzer. The expression for NOx ppm is given by[4]:
Rs = (Vc/VRL - 1) × RL (3)
-3.2 + log (Rs) = -2.84 × log (ppm) (4)
where Vc and RL are shown in Fig 3, VRL = Output Voltage, Rs = filament resistance and RL =
10kCalibration is done at 35ºC and 30% RH. Correction for Rs with temperature and humidity is provided in
MQ-135 datasheet [4].
Fig. 8. The calibration response of NOx analyzer for calibrator source.
The HSM-20G humidity module is pre-calibrated and thus can be directly used. The corrections for
temperature that need to be applied for the slope of voltage vs RH line are provided in the datasheet [5].
4. Test Results
The exhaust analyzer has been tested against the standard exhaust emission measurement instruments during
vehicle-operation. A comparison is established in static mode, since the standard instruments were not mountable
on the vehicle. The comparison is done at 4 throttle levels of the engine. The vehicle that is used here is an All-
Terrain Vehicle, developed in IIT Bombay, which operates on the Briggs and Stratton 10HP Engine (Model No.
20S232 0036). The standard instrument used is the Multi Gas Analyzer by NETEL, India (Model No. NPM-
MGA-2) [7] which does Electrochemical cell based measurement. The measurements performed by the custom
developed exhaust analyzer and those by the standard instrument at the same point of measurement matched
within 20% error. A picture of the test is shown in Fig. 9.
Fig. 9a. The exhaust analyzer test setup. Fig. 9b. The standard instrument

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Fig. 10. Test result for CO measurement test during vehicle operation
Similarly, NOx values for 4 levels of throttle are tabulated in Table 2. RH values are directly indicated in Fig.
12 at respective throttle levels. It has been assumed that the gas present at the point of measurement constitutes
mainly effluent from the exhaust since the air will be driven out due to exhaust flow and thus maintaining the
proportions in the exhaust constant.
. Table. 1. Variation of CO PPM with Throttle
Throttle Avg. CO ppm
1 5200
2 4200
3 4100
4 4100
Fig. 11. Test result for NOx measurement at 4 throttle levels
5. Conclusion and Future Work
The established analyzer reduces the cost of drivetrain parameter tuning significantly. The entire cost of the
analyzer is less than USD100, yet provides a reasonable accuracy of the measurements for the exhaust. This
setup can expedite the research developments in design of green vehicles in university setting. Although it has
been observed that devised exhaust analyzer setup provides a good consensus with the standard instrument, it is
important to incorporate flow rate sensors at the beginning of primary and secondary tubing, which will help in
TABLE 2. VARIATION OF NOX PPM WITH THROTTLE
Throttle Level Avg. NOx ppm
1 29
2 27
3 26
4 20
Fig.12. Test result for RH measurement at 4 throttle levels

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quantifying dilution factor. Also the CO sensor used here requires a heating cycle of 2.5 minute which is
undesirable. It is also necessary to monitor CO2 percentage for complete study of fuel combustion.
References
[1] Real-time portable exhaust analyzer, Argonne National Laboratory,
http://web.anl.gov/techtransfer/pdf/fact_sheets/Exhaust_Analyzer.pdf
[2] Emissions, Toyota Motor Sales, USA, Inc., http://www.autoshop101.com/forms/h56.pdf
[3] MQ-7 sensor datasheet: https://www.sparkfun.com/datasheets/Sensors/ Biometric/MQ-7.pdf
[4] MQ-135 sensor datasheet: http://www.futurlec.com/Datasheet/Sensor/MQ-135.pdf
[5] HSM-20G : http://aitendo3.sakura.ne.jp/aitendo_data/product_img/parts/sensor/HSM-20G/HSM-20G.pdf
[6] Maneerat Ongwandee and Wilas Pepithakul, “Air pollutant emissions from the burning of incense, mosquito coils, and candles in a
small experimental chamber,” J. Environ. Res. 32 (1): 69-79
[7] Multi Gas Analyzer, NETEL, India, Ltd. http://www.netel-
india.com/PRODUCTS/AUTOMOTIVE/MULTI%20GAS%20ANALYZER%20II.pdf