Exhaust Emission and Testing

Herbert Thivakar.A 1

1. Introduction 2. Basic Chemistry of IC Engine Emission 3. Emission From SI Engine 4. Emission From CI Engine 5. Emission Legislation, certification and Test Process 6. Legislation Classification 7. Homologation 8. Principles of Particulate Emission Measurements 9. Principles of measurement and analysis of the Gaseous Emission 10 . Overview about Dynamometer , Chassis Dynamometer and Gas Chromatography

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A majority both vehicle and engine development and of routine testing is concerned with Environmental Legislation directed primarily towards the limitation and controls of the Engine Emission Engine Emission products : 1. HC 2. CO 3. CO2 4. NOx 5.

PAH (Polyaromatic Hydrocarbons)

(Benzene,Formaltihyde,1,3

Butadiene) The Various Harmful results of atmospheric pollution on the environment in generally , and human health in particular.

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1. HC – Hydrocarbons (THC) formed by the Unburnt Fractions of the liquid Fuels. 2. CO – Carbon Monoxide , a highly Toxic Odourless gas 3. C

– Carbon , Experienced in the Form of Smoke

4. NOx – Nitric Oxide and Nitrogen Dioxide , together considered as NOx

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Relation between exhaust emissions and air/fuel ratio for gasoline engines

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Three-way Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2 Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2 Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 + 2xO2 → xCO2 + 2xH2O 7

1. SO2 Sulphur Dioxide 2. it is always operate with considerable excess air , so the CO emission is not a significant problem 3. NOx 4. Diesel Particulate matter 90% of particle emitted by a modern Diesel Engines may be below 1µm size which challenges the tool use to measure their presence

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Two-way A two-way catalytic converter has two simultaneous tasks: Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2 Oxidation of unburnt hydrocarbons (unburnt and partially-burnt fuel) to carbon dioxide and water: CxH2x+2 + 2xO2 → xCO2 + 2xH2O (a combustion reaction) This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon and carbon monoxide emissions. They were also used on spark ignition (gasoline) engines in USA market automobiles through 1981, when the two-way converter's inability to control NOx led to its supersession by three-way converters.

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1. ECE – Economic Commission For Europe and the European union (EU) 2. CARB – California Air Resources Board – produced tail pipe emission standards for Hydrocarbons and CO 3. EPA – Environmental Protection Agency

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1. Test Cycles describes the operation of the tested vehicle or Engine for light duty vehicles , it simulates the actual driving on the road in that it defines a vehicle velocity profile over the test time. For heavy duty and offroad engines, where only the engine is tested on the Engine dynamometer . The test cycles defines a speed and torque profile over the test time . 2. Test procedure defines in detail how the test is executed . Which measurement method and which test system have to be used. It defines the test condition and result calculations to apply. 3. Test limits, Which Defines the maximum allowed Emission of the regulated Components in the engine exhaust. For light duty vehicles , the limit is expressed in the mass per driving distance (g/km). For heavy duty vehicles the limits are expressed in the mass per unit of

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Common classification is by Vehicle Size rather than Engine Size and Type , the main Classification are

1. Light Duty- Gasoline 2. Light Duty – Diesel 3. Heavy Duty

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• Category M: Motor vehicles with at least four wheels and used for the carriage of passengers. • Category M1: Vehicles used for the carriage of passengers and comprising no more than eight seats in addition to the driver’s seat. • Category M2: Vehicles used for the carriage of passengers and comprising no more than eight seats in addition to the driver’s seat and a maximum mass not exceeding 5 tonnes. • Category M3: Vehicles used for the carriage of passengers and comprising no more than eight seats in addition to the driver’s seat and a maximum mass exceeding 5 tonnes. • Category N: Motor vehicles with at least four wheels and used for the carriage of goods. • Category N1: Vehicles used for the carriage of goods having a maximum mass not exceeding 3.5 tonnes. • Category N2: Vehicles used for the carriage of goods having a maximum mass exceeding 3.5 tonnes and not exceeding 12 tonnes. • Category N3: Vehicles used for the carriage of goods having a maximum mass exceeding 12 tonnes.

Weight Classification • Class I RW ≤1305 kg • Class II 1305 < RW ≤ 1760 kg 13 • Class III 1760 kg < RW

1. Low Emission Vehicle (LEV) 2. Ultra Low Emission Vehicle (ULEV) 3. Super Ultra Low Emission Vehicle (SULEV) 4.Transitional Low Emission Vehicle (TLEV) 5. Zero Emission Vehicle (ZEV) 6. Partial Zero Emission Vehicle (PZEV)

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The first Indian emission regulations were idle emission limits which became effective in 1989. These idle emission regulations were soon replaced by mass emission limits for both gasoline (1991) and diesel (1992) vehicles, which were gradually tightened during the 1990’s. Since the year 2000, India started adopting European emission and fuel regulations for four-wheeled light-duty and for heavy-duty vehicles. Indian own emission regulations still apply to two- and three-wheeled vehicles.

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there is emission legislation covering the condition of cars in the population as they age Such tests are required annually and range from a single visual smoke check, through a check at fast idle for levels of CO and HC, to a test under light load on a rolling road that checks CO, CO2 and HC.

Engine warmed up Fast idle 2500–3000 r.p.m., CO no more than 0.3 per cent, HC no more than 200 p.p.m. Lambda between 0.97 and 1.03 Normal idle 450–1500 r.p.m., CO no more than 0.5 per cent. 19

Homologation is a term widely thought to be exclusively involved with certification to emission legislation; in fact it is another case of a word, having originally no particular engineering associations, being taken over and given a specialized meaning. Knowledge of and compliance with the legislative requirements of different markets, covering exhaust emissions but also safety, fuel consumption rates, noise vibration and harshness, competitive benchmarking, etc., is an important aspect of the problem of gaining acceptance of a given product. For the engine or vehicle manufacturer, homologation is a complex and expensive area of activity since all major versions, and all derivatives, of the vehicle must meet the formal requirements that are in force in each country in which the vehicle is to be sold. Homologation is the process of establishing and certifying this conformity, both for whole vehicles and for components. 20

Particulates, when they appear to the human observer, are called ‘smoke’. Smoke colors are indicative of the dominant source of particulate: • black=‘soot’ or more accurately carbon, which typically makes up some 95 percent of diesel smoke either in elemental, the majority, or organic form; • blue=hydrocarbons, typically due to lubricating oil burning due to an engine fault; • white=water vapour, typically from condensation in a cold engine or coolant leaking into the combustion chambers – white smoke is not detected by conventional smoke meters; • brown=NO2 may be detected in exhaust of heavy fuel engines. 21

Opacimeters - that measure the opacity of the undiluted exhaust by the degree of obscuration of a light beam. These devices are able to detect particulate levels in gas flow at lower levels than the human eye can detect. The value output is normally in percentage of light blocked by the test flow. Zero being clean purge air and 100 per cent being very thick black smoke. Smoke meters- that perform the measurement of the particulate content of an undiluted sample of exhaust gas by drawing it through a filter paper of specified properties and estimating the consequent blackening of the paper against a pristine paper. The value output is in some form of ‘smoke number’ specific to the instrument maker. The ever lower particulate emissions from engines has required a new generation of ‘micro soot’ devices capable of detecting particulate levels down to typically 5g per m3 of exhaust gas. These devices incorporate a laser and work on a photo-acoustic principle.

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1.Non-dispersive infrared analyzer (NDIR) Called ‘non-dispersive’ because all the polychromatic light from the source passes through the gas sample before going through a filter in front of the sensor, whereas' dispersive’ instruments, found in analytical laboratories, filter the source light to a narrow frequency band before the sample. The CO2 molecule has a very marked and unique absorptance band of infrared (IR) light that shows a dominant peak at the 4.26m wavelength which the instrument sensor is tuned to detect and measure. By selecting filters sensitive to other wavelengths of IR, it is possible to detect other compounds such as CO and other hydrocarbons at around 3.4m (see Fourier transform infrared analyzer, below). Note that the measurement of CO2 using an NDIR analyzer is cross-sensitive to the presence of water vapour in the sample gas. 2. Fourier transform infrared analyzer (FTIR) This operates on the same principle as the NDIR, but performs a Fourier analysis of the complete infrared absorption spectrum of the gas sample. This permits the measurement of the content of a large number of different components. The method is particularly useful for dealing with emissions from engines burning alcohol-based fuels, since methanol and formaldehyde may be detected. 23

Chemiluminescence detector (CLD) Chemiluminescence is the phenomenon by which some chemical reactions produce light. The reaction of interest to exhaust emissions is NO+O3→NO2+O2 →NO2+O2+photon The nitrogen compounds in exhaust gas are a mixture of NO and NO2, described as NOx. In the detector, the NO2 is first catalytically converted to NO and the sample is reacted with ozone which is generated by an electrical discharge through oxygen, at low pressure in a heated vacuum chamber. The light is measured by a photomultiplier and indicates the NOx concentration in the sample. A great deal of development work continues to be carried out to improve chemical reaction times which are highly temperature-dependent, and so shorten instrument response times. 24

Flame ionization detector (FID) The FID has a very wide dynamic range and high sensitivity to all substances that contain carbon. The operation of this instrument shown schematically in Fig. depends on the production of free electrons and positive ions that takes place during the combustion of hydrocarbons. If the combustion is arranged to take place in an electric field, the current flow between anode and cathode is closely proportional to the number of carbon atoms taking part in the reaction. In the detector the sample is mixed with hydrogen and helium and burned in a chamber which is heated to prevent condensation of the water vapour formed. A typical, sample to measurement, response time is 1–2 s.

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Paramagnetic detection (PMD) analyzer PMD analyzers are used to measure oxygen in the testing of gasoline engines. They work due to the fact that oxygen has a strong paramagnetic susceptibility. Inside the measuring cell, the oxygen molecules are drawn into a strong inhomogeneous magnetic field where they tend to collect in the area of strongest flux and physically displace a balanced detector whose deflection is proportional to oxygen concentration. Since NOx and CO2 show some paramagnetic characteristic, the analyzer has to be capable of calculating compensation for this interference.

Mass spectrometer These devices, not yet specified in any emission legislation, are developing rapidly and can distinguish most of the components of automotive engine exhaust gases; currently they remain an R&D tool, but may represent the future technology of general emission measurement.

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In an advanced test facility such as those involved with SULEV development, there will be three to five tapping points created in the vehicle system, from which gas may be drawn for analysis such as 1. exhaust gas recirculation sample (EGR); 2. before the vehicle catalytic converter (pre-CAT); 3. after the vehicle catalytic converter (post-CAT); 4. tail pipe sample (modal); 5. diluted sample (sample bags). From 2 and 3 the efficiency of the catalyst may be calculated.

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Temperature soak areas for legislative testing Temp -7deg soaking 12 hrs urban driving cycle (UDC) 6 h - 20–30C.

95kmph(MIDC)

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1. a cold-start (505-s) phase known as bag 1; 2. a hot-transient (870-s) phase known as bag 2; 3. a hot-start (505-s) phase known as bag 3.

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Notation Air to fuel ratio AFR Clean Air for Europe (EEC program) CAFÉ Compression ignition (engine) CI Compressed natural gas CNG Critical flow orifice CFO Continuously regenerating trap (diesel particle filter) CTR Constant volume sampling CVS Direct injection DI Reference fuel with a total aromatic content of × wt-% DIR-x Diesel particulate filter DPF Diesel particulate matter DPM Elemental carbon EC Environmental Protection Agency (USA) EPA Heavy duty HD Indirect injection IDI Light duty LD Organic carbon (bound in hydrocarbon molecules) OC Horiba analyser range trade name MEXA™ Polyaromatic compounds PAC Polyaromatic hydrocarbons PAH Particles in the size below 10m PM10 Soluble organic fraction SOF Toxic equivalence factor TEF

1. Air Pollution from Motor Vehicles: Standards and Technologies for Controlling Emissions, World Bank (ISBN: 0821334441).

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Email : [email protected] 36