The following points highlight the top four ways to check and reduce vehicular emissions. The ways are: 1. Inspection Procedure for Gasoline Vehicles 2. Inspection Procedures for Diesel-Fueled Vehicles 3. Road Side Surprise Inspection 4. Remote Sensing of Vehicle Emissions.
Way # 1. Inspection Procedure for Gasoline Vehicles:
The most-common inspection test for a gasoline vehicle involves measuring CO and HC emissions when the vehicle is idling. In the United States and European countries, this test has been supplemented with a second measurement when the engine is running at 2,500 rpm with no load. This test, although appropriate for older model vehicles equipped with mechanical carburetors or fuel injection systems, does not give satisfactory results for vehicles using electronic air-fuel ratio control systems.
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To improve its effectiveness, the idle/2500 rpm test procedure was modified requiring preconditioning of the vehicle at 2500 rpm for three minutes with no load. This preconditioning helps to ensure that the control system in the normal closed loop catalytic converter is adequately warmed up. Even though adequate preconditioning minimizes false failures and improves reliability, the correlation between idle/2500 rpm test (even with preconditioning) and actual emissions were observed to be poor.
Studies in California and Europe indicates that more representative test procedures requiring dynamometer loading of vehicles give substantially better results, especially for NOx emissions. Advanced “short” tests require a vehicle to simulate more rigorous driving conditions on a dynamometer under a loading similar to that which the vehicle would experience in actual driving. Those procedures involve testing the vehicle under simulated transient driving conditions, using equipment similar to that used for new vehicle emissions certification.
U.S IM 240 test, is a 240- second (6 minutes) test and involves operating the vehicle over a transient driving cycle, simulating the stop-and-go of real driving. A recent study concluded that this test is about three times more accurate in identifying vehicles exceeding emission standards than the idle test.
Since the emissions measured in the test procedure are representative of those produced in actual driving, errors of omission and commission are greatly reduced. This reduces the opportunities of fraud and error in the I & M programme. International experience with gasoline vehicles has amply demonstrated that dynamometer tests are essential to minimize false passes. The dynamometer tests should test CO, HC, NOx and PM emissions.
Way # 2. Inspection Procedures for Diesel-Fueled Vehicles:
Emerging evidence about the negative effects of particulate matter in general and fine particulates in particular, demands that inspection procedures for measuring emissions from in-use diesel vehicles should focus on fine particulates. Ideally, diesel vehicles that emit disproportionately high levels of fine particulate matter should be identified and required to be repaired.
Identifying those vehicles that are high particulate emitters, however, is problematic; because the test procedures currently used in the emissions inspection test centers do not readily identify mass particulate emissions. Black smoke and smoke opacity in the diesel exhaust is considered as a proxy or surrogate for particulate emissions and measured in in- use diesel vehicles.
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Smoke from diesel vehicles is usually measured by Bosch and Hatridge methods. In the Bosch method, a spring loaded sampler pulls a fixed volume of smoke through a filter paper depositing the smoke particles on the paper. The paper is then read by a photoelectric device, which produces a number indicating the degree of blackness of the collected particulate matter. Darker the smoke, higher the number.
The Bosch method provides an accurate measure of soot and other dark material in the smoke, but it responds poorly, if at all, to smoke particles that are not dark or black. Engine oil droplets, for instance, produce a bluish or greyish smoke, which have little colour in themselves.
Engine oil smoke is a major contributor to total particulate emissions from diesel vehicles in developing countries including India. Because it fails to detect the smoke from engine oil, the Bosch method correlates poorly with actual particulate emissions from in-use vehicles especially in developing countries like India.
An opacimeter is considered better for measuring the particulate emissions. An opacimeter measures the attenuation of a beam of light shining across the smoke plume in percent opacity. Since opacimeters include the effects of both black smoke and grey or white smoke from engine oil, they provide a better indication of emissions than Bosch method for diesel emissions in developing countries like India, where engine oil particulates are significant.
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Hence most of the developing countries which were using Bosch method switched over to opacimeters. Hartridge meters measure the opacity of the smoke. India has been following Hartridge method from the start to measure emissions from in-use diesel vehicles.
The most common procedure for testing emissions from in- use diesel vehicles is the snap (also called free) acceleration test defined in ECE R24 European standards. The test specifies that, with transmission in neutral, the throttle pedal should be pushed rapidly but not abruptly to its full throttle position, accelerating the engine from low idle to its maximum governed speed. This is repeated several times and the average of the maximum exhaust gas opacity in each test is computed.
Even when properly administered, smoke/opacity tests have two short comings-reproducibility and correlation to particulates. Recent studies indicate a very poor correlation between visible smoke measured using free acceleration method and mass particulate emissions measured in a dynamometer test using a realistic drive cycle.
The study indicated that a number of high particulate emitters have quite low scores on smoke emissions in free acceleration test, while some “high smokers” have relatively low particulate emissions compared to the true gross polluters. Hence free acceleration tests run the danger of misclassifying gross polluters as relatively clean and low polluters as high polluters. In another recent study in heavy diesel vehicles, particulate emissions decreased by 38% on average after repairs but opacity readings increased by 29%.
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Studies reveal that free acceleration tests cannot be viewed as a means of identifying high particulate emitters, but rather as diagnostic tests to identifying malfunctioning and defects among older engine vehicles with mechanically controlled fuel systems. Free acceleration smoke tests are not at all effective for modern, electronically controlled engines or turbo-charged engines with boost control. For these vehicle categories, an alternative test procedure has to be identified.
Studies to date suggest that dynamometer- based load tests are needed. However in view of the exhorbitant costs involved in setting up dynamometer-based tests, free acceleration tests will continue to play an important role in emission testing programmes in India and the other developing countries for the foreseeable future.
However modern engine vehicles as well as high annual mileage commercial vehicles like buses can be tested on dynamometer to stricter standards and for rest of the vehicles free acceleration system can be continued.
Way # 3. Road Side Surprise Inspection:
Road side surprise inspection programmes are a good supplement to periodic Inspection and Maintenance. Road side inspections involve stopping vehicles that appear to emit excessive amounts of emissions and smoke and testing the exhaust emissions.
A member of the inspection team observes on coming vehicles visually, and waves over those producing excessive emissions. The vehicles that pass the test are allowed to go and those that fail get a challan and will be asked to get the repairs done.
Vehicles found to be in violation of emission standards are fined and or prohibited from circulation till the repairs are carried out. Severe fines are imposed for second and third offenses and if repairs are not carried out within the time limit stipulated in the challan.
Singapore, Mexico, Thailand, California State in U.S.A effectively utilize the road side inspections for emissions control. This programme is especially useful in controlling emissions from diesel buses and trucks. Because of the surprise nature of these inspections, it is difficult for the vehicle operators to readjust the tampered or damaged emission control systems like carburetors or fuel injection pumps.
Periodic inspection is predictably scheduled, giving vehicle owners an opportunity to evade the programme. For instance, one common cause of high smoke emissions in diesel engines is tampering with the maximum fuel setting on the fuel injection pump. This provides more fuel to the engine, increasing power output and smoke.
Since vehicle owners know when the vehicle will be inspected, they can adjust the pump to its proper setting immediately before the inspection, then return it to higher power setting after wards. Studies indicate that another way of reducing visible smoke is putting a handful of gravel in the exhaust pipe just before the inspection. Similar tricks are possible, and reportedly common, for meeting carbon monoxide emissions with gasoline engined cars and two wheelers.
Since a vehicle owner cannot predict whether he will be targeted by a road-side inspection, such inspections are difficult to evade. Since gasoline vehicles with high hydrocarbon and carbon monoxide emissions are not usually as obvious as the diesel vehicles producing black smoke, these programmes must rely on stopping vehicles at random. This reduces the efficiency of the programme and increases the inconvenience to drivers of low-emitting vehicles. Remote sensing programs can increase the effectiveness of road side inspections.
Singapore has one of the most effective road side inspection programmes. In Singapore, the passing standard for the diesel smoke is 50 Hartridge Smoke Units (HSU). While the periodic routine tests are carried out, Singapore concentrates on road side enforcement as an effective deterrent to smoke emissions, particularly from heavy-duty vehicles. During road side inspections, if the smoke level is less than 50 HSUs no action is taken.
If it is more than 50 HSUs the action is as follows:
British Columbia State in Canada has evaluated the cost effectiveness of several alternatives of emissions controls for heavy duty vehicles and out of the various options available, road side smoke inspection appeared to be the least capital intensive and the most cost effective.
Way # 4. Remote Sensing of Vehicle Emissions:
Remote sensing of vehicle emissions is a new technology, and has been in operation in many cities throughout the world to improve the effectiveness of vehicle emissions control programmes. The technique works by measuring the absorption of a beam of infrared light by carbon dioxide, carbon monoxide, and hydrocarbons in a vehicle’s exhaust.
Based on the absorption, a computer is able to calculate the ratios of carbon monoxide and hydrocarbons to carbon dioxide in the exhaust of a vehicle. It is possible to instantaneously know the concentrations of pollutants as a vehicle passes the remote sensing device.
The major limitation is that the remote sensing device can measure only one lane, and the sensor beam should not be blocked by pedestrians, bicycles etc., Remote sensing cannot identify evaporative emissions. The system does not work on vehicles with elevated exhaust pipe discharge.
Other major limitation is that even properly functioning vehicles may exhibit high carbon monoxide and hydro carbon concentrations at idle. Some older vehicles experience high hydrocarbon emissions during deceleration, while newer vehicles cut off fuel during deceleration making the hydrocarbon to carbon dioxide ratio hard to predict. Also hydro carbon concentrations exhibited by two- stroke two wheelers in normal operation would indicate gross malfunction in a four-stroke engine.
Identifying cases in which unusually high hydro carbon and carbon monoxide conditions are caused by normal cold-start enrichment is more difficult. It may be more practical to locate the sensors where vehicles would have operated for several minutes before passing the sensor location, to avoid this problem.
The main advantage of remote sensing is that it can screen large number of vehicles quickly and cheaply. It also provides an unbiased indication of vehicles on the road that fall into different emission classes. Remote sensing can thus supplement periodic Inspection and Maintenance and road side inspection programmes.
Remote sensing could help to identify some gross-emitting vehicles that evade the periodic Inspection and Maintenance tests as well as the vehicles that pass the I & M test because of tampering with the emission controls.
For remote sensing to achieve its potential, a number of technical issues needs to be addressed. The most critical of these is improving the accuracy of remote sensors in identifying high emitters. Another problem that needs to be solved is sampling across multiple-channels of traffic without causing a safety hazard.
The remote sensing system should also be capable of operating for long periods unattended in order to save labour costs and reduce conspicuousness of the testing system. Hence they are normally located behind traffic signs or in some inconspicuous place.