Ultra fast-response gas analyzers

Ultra fast-response gas analyzersFor transient HC, NOX, CO & CO₂ exhaust, intake and in-cylinder applications

• Cold start engine calibration• Real-time EGR control refinement• Transient fuelling control• Combustion refinement• Transient catalyst evaluation• Direct in-cylinder measurement• Scavenging and gas exchange studies• T< 0° C sampling

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Flame arrival

Rapid burn-down

Burned gas

Post-flame hydrocarbons from crevices etc.

Signal invalid during intake stroke

Pre-flame mixture HC concentration

Cylinder pressure(for indication)

PFI gasoline [HC] at spark plug, idle

Crank angle degrees ATDC

[HC]

(ppm

C₃)

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2.35 2.355 2.36 2.365 2.37 2.375 2.38 2.385 2.39 2.395 2.4

Exhaust valve opens Exhaust valve closes

Scroll-up HCs from cylinder wall & piston crown are last to exit cylinder

Other crevice or surface HCs are entrained into exhaust flow

Trapped exhaust valve crevice HCs are expelled first

Blow-down and expulsion of burned gas contents from cylinder

GDI exhaust port HC during single exhaust stroke at idle following cold start

Time since engine start(s)

[HC]

(ppm

C₃)

Gas analyzers

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Engine out [HC]Engine speed

1st fuelinjection event

Single injection pulses Split (double) injection pulses

Trapped cylinder contents purge during cranking

Spark retardedto aid catalyst light-off

Individual exhauststroke features visible

Family of fast-responsegas analyzers

HFR500 for fast HCCLD500 for fast NOx (shown here)NDIR500 for fast CO & CO₂

Each gas analyzer is supplied “ready to operate” with two channels as standard. Control via AK protocol, cold temperature operation, in-cylinder sampling hardware and alternative sample probe configurations are all available as options.

Applications

S.I. engine calibrationThe engine start (crank and run-up lasting ~3s) followed by the early portion of a drive cycle requires complete and stable combustion to comply with current and future emissions legislation. With the aftertreatment still in its warm-up phase, the engine-out emissions generally pass untreated into the atmosphere and therefore knowledge of the combustion state from each cylinder and every exhaust stroke is desirable. The calibrator’s challenges involve retarded spark timing and multiple injection pulses to promote

catalyst heating, thermal inertia of the turbocharger, cold engine internal surfaces, transient fuelling and VVT system optimization. The introduction of alternative fuels can prove challenging for some existing combustion systems (especially when cold) and alternative engine calibrations for fuel injection, spark timing and valve timing can be developed using this equipment.

The HFR500 fast FID is effective at identifying such transient events as partial burns and exhaust valve leakage, whereas the NDIR500 fast CO & CO₂ analyser can be used for ultra-fast measurement of combustion λ derived from the relationships of CO & CO₂ emissions vs AFR.

Engine out HC during cold start on a 1.6 Litre GDI engine

[HC]

(ppm

C)

Engine speed (rpm)

Time (s)

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210 212 214 216 218 2200.96

0.98

1

1.02

Poor NO conversion during lean half-cycles due to aged catalyst with poor oxygen storage

Time since start (seconds)

[NO

] (pp

m)

λ

Vehicle Speed

Slow NO Engine-out

Fast NO TailpipeFast NO Engine-out

Fast NO Engine-outFast NO Tailpipe

Lambda

Transient NO measurement 200 – 305 seconds of FTP75 drive-cycle

Time since start (seconds)

Vehicle Speed (mph)

[NO

] (pp

m)

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[NO]Cylinder Pressure

Fast NO measurement in the exhaust port of an SI enginehigh load, 1,500 RPM, λ=1

Time (ms)

[NO

] (pp

m)

Cylinder Pressure (bar)

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121 122 123 124 125 126 127 128-2,400

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0CO2 at Intake Port 1CO2 Post EGR ValveAverage Speed (kph/2)EGR Valve Drive Pressure

EGR valve closes EGR valve re-opens

EGR valve closes, then re-opens during gear change

~1s delay before EGR reaches intake port

720° single intake stroke

EGR delay during gear change on a diesel passenger car

Time (s)

EGR Valve D

rive Pressure (mbar)CO

₂ (%

) & V

ehic

le S

peed

(kph

/2)

Catalyst and after treatment evaluationThe performance of catalytic converters is crucial to modern emissions legislation compliance and an understanding of the dynamic processes involved in their operation is required. Critical aspects such as light-off at cold start, O₂ storage under transient conditions, catalyst damage, flow effects and cylinder imbalance are studied from the perspective of fast gas concentration changes entering and exiting the aftertreatment system. Volume engine producers also have a strong interest in cost reduction through reducing the use of precious metals as catalyst coatings and therefore optimizing the catalyst’s position, size and control of engine-out gases. The fast gas analyzers’ sample probes may also be used to traverse across the front and rear faces of aftertreatment systems to check for spatial variations in conversion efficiency.

Even after the catalyst is warm, the measurement and control of NOX in diesel engines via EGR or de-NOX aftertreatment, plus

general engine control during speed and load changes require careful calibration to avoid pollutant breakthrough or catalyst damage. Fuel economy measures such as stop/start and cylinder deactivation are also highly transient features which need careful calibration/optimization later in the drive cycle.

EGR system development and controlThe advent of low-pressure EGR systems promises durability and efficiency benefits over existing high-pressure EGR systems. However, the control of EGR delivery rate remains complex over the engine’s operating envelope; an existing challenge for both high- and lowpressure EGR systems. The accurate and timely delivery of the correct amount of EGR is vital for both NOX and particulate control. The NDIR500 is widely employed for the realtime measurement of EGR at various points within the EGR circuit. Transient delays and imbalances in EGR to any particular cylinder can be closely studied and the calibration

Combustion refinement and cyclic variabilityExhaust port measurement of cycle-by-cycle HC, NOX, CO or CO₂ emissions provides insights for combustion refinement programs. The emissions from each cycle are often considered together with cylinder pressure data to enhance understanding of gas exchange, combustion and pollutant formation processes. Comparison of pollutants emerging from each cylinder during engine transients can reveal AFR imbalance (e.g. where although the total engine-out is stoichiometric at λ=1, some cylinders emit high CO and some low). Transient imbalance of EGR between cylinders is also a concern and the NDIR500’s ability to sample from low intake pressure environments is a useful feature for this application.

thereby improved. The NDIR500 can also identify intermittent performance problems (such as sticking or blocked EGR valves).

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Cambustion Fast NOXConventional NOXBrake Torque

NOX engine-out generally following torque

Conventional analyzer delay of ~4s

Double - peak smoothed by bench analyzer’s slower response

Interesting drop in NOX just prior to load. Perhaps due to increased fuelling affecting AFR (e.g. rich excursion)?

NRTC excavator Tier 4 engine sampling engine – out gas

Time (s)

Torque (Nm

)NO

x (pp

m)

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Engine-out HCAverage speed

[HC]

(ppm

C₃)

Vehicle Speed (kph)

Time (s)

Split injection strategy and retarded spark timing for rapid catalyst light-off produces poor combustion here

Cold start and run-up to idle

Rich excursion at 1st acceleration

Downsized turbo GDI 1.6 litre, EURO IV passenger car cold start HC emissions

LNT and SCR system developmentLean NOX Traps (LNTs) and Selective Catalytic Reduction systems (SCR) benefit from analysis through the use of fast gas analyzers. LNT purge is a particularly transient phenomenon where accurate control of reductants and termination of purge to minimise CO breakthrough is critical. Some systems involve very rapid rich-lean oscillations (e.g. for de-SOX), the dynamic effects of which are too rapid for standard emissions benches to record accurately. Optimization of SCR systems via accurate measurement and prediction of engine-out NOX is important to enhance the accuracy of urea dosing, to allow elimination of an ammonia slip catalyst.

Single exhaust stroke analyses – base engine designThe ability to measure with such a fast time response offers a unique insight into the characteristics of a single exhaust stroke. For example, the effects of intermittent exhaust valve leakage are visible as unburned HCs appearing in the exhaust port before

EVO (Exhaust Valve Open) and the effects of ring-pack and top-land geometry affect the amount of scroll-up HCs at the end of the exhaust stroke. [See GDI Exhaust Port HC chart on front cover].  Such measurements are only possible with an ultra fast-response FID

Advanced engine developmentDownsized turbocharged GDI engines are widely adopted by OEMs in the pursuit of improved fuel efficiency without compromising power. The highly developed combustion strategies employed have often been researched using Cambustion equipment (both gas and particulate analyzers). Challenges associated with cold start fuel vaporisation, catalyst heating strategies, poor combustion and the possible future adoption of more transient test cycles all require fast-response analysis to facilitate a comprehensive understanding of the processes involved.

The control of advanced combustion concepts such as HCCI, CAI, stratified GDI and Miller cycles benefits from measurement of exhaust and intake port gases on fast timescales to study the gas exchange processes, cyclic variability and complex engine control requirements.

In-cylinder sampling of HC for GDI transient fuelling calibration and cold startsDelivery of the correct quantity of fuel to the spark plug is of vital importance at all operating conditions but is a particular challenge during transients and at cold start. Sampling through a specially modified offset spark plug at moderate engine speeds (up to 1,500rpm), the HFR500 fast FID can measure [HC] within a few millimetres of the spark plug’s electrodes and provide information on transient fuel delivery to aid more stable combustion.

Rigid Tip of Heated Sample Probe Cam Covers

Inlet Cam Exhaust Cam

SSP BodyOffset sampling spark plug Heated sampling probe in situ

In-cylinder measurement of residual burned gases

The control of the residual burned gas content of an engine’s charge is being increasingly exploited as an effective way of suppressing NOX formation and for the operation of advanced combustion concepts such as HCCI and CAI. For engine speeds below 1,500 rpm, the NDIR500 can be used for direct in-cylinder measurement of CO2 – aiding in the development of VVT calibrations, transient engine operating parameters, cylinder deactivation studies and cyclic variability issues.

AccessoriesEach gas analyzer is supplied standard with 2 independent channels including sample heads fitted to 10 metre (30ft) conduits. A tool and spares kit to match the anticipated needs of the first year of operation and a set of in-line sample filters are also included. The

sample filters have a typical soot capacity of 5 hours at an average 10 mg/m3 soot concentration (corresponds to 2 g/h soot output at an exhaust flow of 250 kg/h). Other available accessories include heated sampling system conduits (for T<0 ° C sampling), control via AK protocol, in-cylinder or intake sampling hardware, extended warranty and custom length sample probes.

Anatomy of an in-cylinder CO₂ trace (1.8-litre PFI gasoline engine at idle)NDIR500 Fast CO & CO₂ measured through sampling spark plug

Time (s)

CO₂ (

%)

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0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

CO2 produced by flame passing over spark plug sampling point

Sample transport delay CO2 in residual gas New sample gas is delivered to NDIR500 sample head near end of compression stroke

In-cylinder CO2Cylinder Pressure

Blow-throughand scavengingThe control of residual burned gas in downsized turbocharged GDI engines is especially important at low speed and high load conditions where valve overlap is increased to purge residuals from the combustion chamber. However, the short-circuited air which accompanies this scavenging process during short duration accelerations can cause the exhaust gas to be “lean” and causes NOX breakthrough to the tailpipe of the 3-way catalyst.

Engine-out LambdaTailpipe Lambda

Engine-out [NO]Tailpipe [NO]

Throttle Pedal (0-1)

Tailpipe breakthrough of NO due to blow-through at high load/low rpm

Blow-through causing NOx breakthrough2.0L Euro 6 turbocharged GDI engine during WLTC

Time (s)

Lam

bda

/ Thr

ottle

Ped

al (0

-1)

Fast [NO

] ppm

Small engine development Current and expected emissions legislation for powered twowheelers and small utility engines is driving development of advanced combustion and aftertreatment systems, with focus on lowest-cost solutions. The relatively low sample flow rates and Cambustion’s unobtrusive sample probe sizes allow easy sampling from small engines. The fast response time is particularly beneficial at high engine speeds. Customer perception of quality is often derived from the “easy start” of a small engine - especially where a manual kick or pull start is employed. The delivery of an acceptable concentration of fuel to the spark plug at cold start is a good application for the fast FID. The generally lower-cost components can also lead to issues such as intermittent exhaust valve leakage and cyclic variability. Exhaust port sampling of HC can help identify such fast transient problems.

Fuel delivery to plug from cold startMeasured with fast FID through o�set spark plug hand-pull start 50cc engine

Time (ms)

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[HC] at λ=1[HC]Spark

[HC]

(ppm

C₃)

Specifications HFR500 HC analyzer CLD500 NOX analyzer NDIR500 CO and CO₂ analyzer

Measurement principle Flame Ionisation Detector Chemiluminescence Detector Non-Dispersive Infra-Red

Component(s) measured Total Hydrocarbons (THC) NO, NO2 (with NO₂ converter) Carbon monoxide (CO), Carbon dioxide (CO₂)

Number of channels 2 2 2

Measurement ranges 0-2000 to 0-1,000,000 ppm C1 0-100 ppm to 0 -5,000 ppm (extendable to 0 -10,000 ppm)

0-5%, 0-10%, 0-15% and 0-20%

Fastest response time T90-10% (sample probe length dependent)

0.9 ms 2 ms (8 ms with NO₂ converter) 8 ms

Zero drift <1% FS / hour <5 ppm / hour <2% FS / hour

Span drift <1% FS / hour <1% FS / hour <2% FS / hour

Sample gas flow (1 channel including bypass)

6 litres per minute (1 bara) 6 litres per minute (1 bara) 4 lpm with NO₂ converter

6 litres per minute (1 bara)

Power supply 50/60 Hz 100-240 V AC

Max power requirement (single phase)

1.7 k VA 2.6 k VA 1.7 k VA

Gases required (all at 2 bar gauge)

40% H₂/He or H₂/N₂ fuel HC span gas, Zero air and N₂

NO (NO₂) span gas, N₂ 2 each of CO and CO₂ span gases, N₂

Cabinet dimensions (w x d x h) 550 x 780 x 1,140 mm including wheels

Approx cabinet weight (incl. vac pumps)

125 kg 150 kg 125 kg

Operating conditions 0 – 40° C. Sub-zero sampling option available

Conduit length 10 metres (detector to cabinet). Custom lengths available

Connection to control PC RS232 or RS485

Test cell interface Analog data outputs with AK and digital remote control optional

All specifications subject to change without notice

How fast-response gas analyzers workCambustion’s range of fast gas analyzers are based on the industry-standard measurement techniques of: FID (for total hydrocarbons), CLD (for NOX) and NDIR for CO and CO₂. The detectors have been miniaturized and housed in remote sample “heads” close to the sampling point on the engine. This architecture

helps to yield millisecond response times. The analyzers incorporate a constant pressure heated sampling system allowing measurement from fluctuating pressure conditions including those found within the firing engine cylinder. The first of these products was developed in 1987 and fast gas analyzers are currently engaged in a wide range of gasoline, diesel and alternative fuel applications worldwide. See our alternative brochures for Cambustion’s fast particulate products.

Technical papers involving Cambustion fast-response gas analyzersMany hundreds of technical papers involving our products have been produced by Cambustion customers over the years, and many can be found via our website. https://www.cambustion.com/publications The papers cover various applications but please contact us if you have an application about which you’d like more information.

DEC 2020

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