Automotive gas sensors Christophe PIJOLAT, Ecole des Mines de St-Etienne, France
Outline - EC regulation - AQS - Oxygen sensors - DeNOx SCR - NOx and NH3 sensors - Soots sensors Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 2
EC regulation for automotive exhausts Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 3
Heavy-duty diesel powered vehicles and buses Dual problem with particules and NOx Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 4
Comparison of regulations Japan, United States and Europe Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 5
Sensors in automotive applications Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 6
Gas sensors in car applications Air control Flap Fuel injection OBD Fuel tank and canister HC Motor control EGR L.O. TWC DeNOx NOxTrap Gas sensor Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 7
Metal oxide SC sensor O 2 Conductance (Ω -1 ) R RO O - O - O - CH 4 1000 ppm SnO 2-X C 2 H 5 OH 100 ppm E r signal CO 300 ppm Air 200 400 Temperature ( C) Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 8
OutdoorexperimentswithSC sensors: Atmospheric pollution car traffic Urban pollution Evolution of the sensor response on a town road ( downtown Lyon) Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 9
Urban pollution Response of a CO infrared analyser and a SnO 2 sensor during a period of 10 hours in a road tunnel (Lyon - 1990) Conclusion: SnO 2 sensor is OK for CO monitoring.but.. Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 10
Exampleof problemwithinterferinggases: SO 2 (sub-ppm) 1.2 10-3 1 10-3 day n 1 day n 5 day n 10 day n 15 day n 20 untreated sensor 1 10-3 8 10-4 SO 2 treated sensor 8 10-4 6 10-4 6 10-4 4 10-4 2 10-4 4 10-4 2 10-4 day n 1 day n 10 day n 20 0 10 0 0 20 40 60 80 100 120 CO concentration (ppm) 0 10 0 0 20 40 60 80 100 120 CO concentration (ppm) Instability (increase of signal) of a pure SnO 2 sensor during one month experiment in a tunnel Stability of a pretreated ( by SO 2 ) SnO 2 sensor : Response during one month experiment in a tunnel Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 11
AQS / Air Quality System: Traffic pollution: Problem for car indoor air quality Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 12
Dual response with SnO 2 sensors Problem of the dual response with Reducing(CO) and Oxidizing(NO 2 ) gases 12 Sensor Response (10-5 Ohm -1 ) 10 8 air air NO 2 50 ppm air NO 30 ppm 6 Influence of NO 2 (2.5 ppm) on the CO response of a SnO 2 (Pd) 4 2 0 CO 150 ppm 0 4 8 12 16 Time (h) air CH 4 1000 ppm Dual response of a thin film SnO 2 sensor to oxidising (NO 2 ) and reducing gases (CO, CH 4 ). Special behaviour of NO resulting of few ppm NO 2 in the NO injection air Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 13
Use of filter film to control the selectivity Filter Nylon Cap Steel Mesh Nickel Can Pt SiO 2 SnO 2 SiO 2 Chip TO Base Devices with thick films SnO 2 / SiO 2 SnO 2 Substrat Al 2 O 3 20 µm Al 2 O 3 Deposition of a thin film of Rh (10 nm) : no problem with NO 2 Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 14
Automobile: AQS (Air Quality System) DetectionCO / NOx Control flap: open / close Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 15
AQS frommics(ch) (Air Quality System) Silicon micro-hotplate 140 mw Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 16
Example of MiCS dual element sensor output signal whilst driving through polluted roadway tunnels. Note that the reducing and oxidizing sensor signals are complimentary. The flap is closed when both high reducing and oxidizing gases exist. This translates to a high reducing signal level and a low oxidizing signal level Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 17
Otherexamplesof AQS AQS from NTK AQS from Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 18
Automotive exhausts: Post-combustion catalysis Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 19
TWC catalyst(gasoline) and DeNOx(Diesel) DeNOx SCR Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 20
Diesel motors: NOxand particules (leancondition) NOxTrap Two steps: 1 Trap 2 Regeneration Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 21
Oxygen sensors TWC (Three Way Catalytic Convecter) For gasoline motors Need of Oxygen sensors for car exhaust O2 sensorswithysz : first patents near1960 Lambda sensors: more 30 M / year Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 22
Electrochemical (potentiometric) sensors Solid electrolytes: ionic conduction Performances: depend on the quality of the electrolyte and temperature Electrical conductivity: need of doping Zr0 2 (Y) / YSZ 0 Thermo :. potentiel chimique : µ i = µ i + RT log a i µ ~ = AG = 0 0. potentiel électrochimique : µ ~ i = µ i + z { i F φ { x ch arg e potentiel électrique où γ i : coefficient d activité C i : concentration Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 23
Oxygen sensors Zirconia sensors First development of O 2 sensors for industrial application Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 24
Lambda sensor for car exhausts NGK O2 sensors: heated and not-heated Porous protective thick films (problem of soot and water drops) Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 25
Application of Oxygen sensor: control of TWC Catalyser in car exhausts Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 26
Car applications: Need of proportional O 2 sensor for diesel exhaust control Amperometric type: Measure of the current proportionnal to gas reactions at electrodes Anode: CO + O 2- CO 2 + 2e - / Cathode: ½O 2 + 2 e - O 2- Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 27
Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 28
Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 29
NOxand NH 3 sensorsfor SCR: Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 30
NOx sensor Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 31
NOx sensor/ «Sensing» electrodes Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 32
SCR Selective Catalyse Reduction Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 33
Delphi NH 3 AmmoniaSensors NH3 sensing electrode Electrolyte Reference electrode Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 34
Mixte potential NOx sensor: Obtained when the velocities of reducing and oxidizing reactions are equal Mixte potential depends on: Electrochemical kinetics O 2 + 4e - 2O 2 - CO + O 2- CO 2 + 2e - Catalytic activities: adsorption/désorption properties YSZ Au/Pt electrode Pt resistor Dielectric Au YSZ Pt Connection Connection Weld Weld Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 35
Dual responseno / NO 2 Sensor tested at 450 C and under 12%O 2 atmosphere CO, NO and NO 2 are always mixed with air and N 2 to obtain a final O 2 conc. of 12%. Sensor signal obtained V = V Pt V Au CO, NO reductive gas positive response NO 2 oxidative gas negative response Use catalytic filter 100 ppm de NO 2 ou 100 ppm de NO Thermo. NO/NO 2 equilibrium: Influence of catalyst 38 ppm de NO 2 62 ppm de NO Filter at 450 C Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 36
Use catalytic filter for total NOx Protection of the sensing elements Total NO x sensor Elimination of interference gases Impose a NO/NO 2 ratio corresponding to the thermodynamic equilibrium (NO + 1/2O 2 NO 2 ) Preparation of the Pt catalytic layer Mixture: Commercial catalyst 5% platinum dispersed in gamma alumina Test at 450 C Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 37
Use of polarisation V= E 0 + R(YSZ + Au +Pt)i + η Au + η Pt E 0 : potential at curent = 0 R : Resistance i : applied curent η : over-potential Responsesof planarsensorla0.8sr0.2 CrO3/YSZ/Pt (a) open circuit (b) withpositive polarisation (Pt = anode) de 1,4μA à 550 C cathode NO 1 O 2 + 2 e 2 O 2 2 + 2 e NO + O 1 2 2 anode 1 2 2 O O 2 + 2 NO 2 2 + O NO 2 + e 2 NO + 2 e N 2 + O CO + O 2- CO 2 + 2e - 2NO + 2e - N 2 O + O 2- e Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 38
Soot and particles detection: FAP -DPF Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 39
Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 40
Prototype of a soot sensor by Electricfil Exhaust soots carbon Use of electrical properties of carbon Signal readout Soot particle Pt electrodes Ceramic substrate Al 2 O 3 Pt heater Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 41
Soot resistive sensor Engine bench Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 42
Flex Fuel Sensors The so called flexible fuel vehicle (FFV) runs on normal gasoline but also blends of gasoline and ethanol. In the US and Europe E85 is a common fuel which includes 85 % of ethanol and 15 % of gasoline. Resistive sensor QCM sensor Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 43
Hydrogen Sensors Application for H2 leaks with fuel cell SiC FET Sensors for various automotive sensors Christophe PIJOLAT, Ecole des Mines de St-Etienne, France 44