WARNING
Wear safety glasses when using compressed air, as flying dirt particles may cause eye injury.
Fastener Notice:
The first emissions controls implemented in the mid 1960’s consisted of engine modifications and add on pollution control devices. The most widely used emissions control device was the air injection reactor (AIR). This device used a belt driven pump to inject fresh air into the exhaust manifold as a way of diluting the exhaust emissions before exiting to the atmosphere. The other device that came to be was positive crankcase ventilation (PCV) valve. The PCV took blow-by gases that were – until that time—vented to the atmosphere and recycled the gases to the intake manifold to be burned during normal combustion. These pollution control systems moderately lowered emissions, but they also caused a reduction in engine performance and increased fuel consumption if they malfunctioned.
In 1972 the federal government initiated a standardized test procedure for measuring vehicle manufacturers' compliance with federal emissions standards. This test is performed on a chassis dynamometer to provide a consistent and accurate way to measure the amount of HC, NOx, CO, and CO2 that a vehicle produces. This Federal Test Procedure (FTP) applies to both Light-Duty Vehicles (LDV) and Light-Duty Trucks (LDT). Over the years the test procedure has been modified to the support amendments to federal emissions requirements.
The FTP is designed to simulate typical driving conditions in urban areas. This FTP certification is a requirement of all pre-production vehicles that are to be sold in the U.S. Being compliant includes being able to pass the FTP throughout the vehicle's life. Because of this, the FTP is also used in certain states on vehicles used by the general public.
In 1975, two-way catalytic converters were introduced to help lower the emissions of HC and CO. Catalytic converter efficiency of this era was poor and required cumbersome air management systems to provide the oxygen necessary for catalyst conversion. By cleaning-up the exhaust (post-combustion) in addition to the PCV, AIR, and exhaust gas recirculation (EGR) auto manufacturers were able to address the Federal Government's concerns regarding pollution contributed by automobiles, however this did nothing for fuel efficiency. As technology increased and electronic fuel injection was introduced automobile manufacturers’ were finally getting a handle on maintaining emissions control efficiency with better fuel economy and improving engine performance.
The Federal Government's emissions standards combined with the price and availability of fuel created a demand for the auto manufacturers to produce vehicles that were more fuel efficient and produced fewer emissions. At the time, the easiest way to reduce both fuel consumption and vehicle emissions was to lower the engine displacement and maintain higher (lean) air/fuel ratios. Although emissions decreased, these smaller and leaner running engines lacked performance when compared to their predecessors.
These new engine designs running on leaner air/fuel ratios caused combustion temperatures to rise. The increase in combustion temperatures caused a dramatic rise in the production of oxides of nitrogen (NOx).
The air that enters the combustion chamber consists of approximately 79 percent nitrogen, 20 percent oxygen, and 1 percent mixed gases. As the air/fuel mixture enters the combustion chamber and ignition occurs, the nitrogen forms various compounds with the oxygen. These compounds have varying amounts of oxygen and are know as oxides of nitrogen or NOx. of nitrogen are present during all phases of combustion; however, they are developed in large quantities when combustion chamber temperatures reach 2500° F. To help control the high production of oxides of nitrogen, manufacturers began equipping their vehicles with Exhaust Gas Recirculation (EGR) systems in 1973. In addition to the EGR system, manufacturers modified camshaft profiles, retarded ignition timing, and lowered compression ratios to lower NOx emissions.
Emission Control Systems
In order to help reduce emissions and improve fuel economy in the 1980’s, manufacturers began equipping vehicles with three-way catalysts and electronic fuel controls. It was found that the mechanical systems used up until this time could not maintain control to provide the desired 14.7: 1 air fuel ratio that is optimal for catalyst activity. By 1988, the California Air Resources Board (CARB) began regulation of the OBD (On Board Diagnostics) systems sold in California. These OBD systems were designed to monitor fuel, ignition, and emissions system components to determine if they were operating correctly. When a system was found to be operating out of specification, a fault code was stored in the Engine Control Module (ECM). In some cases, a "Check Engine Light" would illuminate. Technicians could connect to the ECM through a Data Link Connector (DLC) and retrieve fault codes.
The new emission control systems were a significant departure from traditional emissions systems. Instead of using mechanical systems to control key engine components, such as the carburetor and ignition system, these components are controlled by an on-board computer typically known as the Electronic Control Module (ECM). The interim fix for the earlier emissions controls was the feedback or electronic carburetor. This carburetor took information from an onboard computer to richen or lean the fuel mixture based on inputs the computer received from various sensors. The development of the feedback carburetor laid the ground work for fuel injection. Control of emissions is now maintained by precise control of the combustion event. Control of emissions is now geared toward the precise tuning of the combustion event for a variety of operating conditions as determined by the ECM. The modern ECM receives input data from specific sensors to determine the course of action. Not only does the ECM read the information and send instructions to maintain performance and emissions efficiency, but it also monitors components for faults and alerts the driver and technician through a CHECK ENGINE light. The technician plugs into the ALDL (alternate location data link) and accesses the ECM to learn of the location of the fault and the diagnostic information to correct the situation. Use of a computer enables faster and more accurate control to minimize vehicle emissions while simultaneously improving engine performance.
In the early 1980’s three-way catalysts were introduced to replace the two-way catalytic converter. Three way catalysts are designed to effectively reduce HC, CO and NOx emissions simultaneously. As with the two-way catalytic converter, proper operation of a three-way catalyst requires precise control over the application of fuel for combustion. If there's too much air, the converter will not reduce NOx emissions. If there's too much fuel, the converter will not reduce HC and CO emissions. . A leaner mixture is hotter than a rich mixture. If the air/fuel mixture were to stay lean for too long a period of time the catalyst would overheat. This cycling of the fuel mixture is intended not only to maintain optimum emissions and performance, it is also designed to maintain and cool the catalyst.
To achieve this precision control electronic fuel injection systems began incorporating an oxygen sensor to help monitor air/fuel ratios. The oxygen sensor has developed over the years to include pre and post catalytic converter locations and the addition of a pre-heater to warm up the sensor to activate the sensor quicker reducing startup emissions. Today’s oxygen sensors are known as wide-band O2 sensors. This intimates that there is a greater degree of monitoring done by the sensor since it can read a much larger scale. When these electronic fuel metering systems use input data from the oxygen sensor, they are operating in "closed loop". On the other hand, "open loop" describes the mode of operation when the system does not use oxygen sensor data to maintain fuel control.
A closed loop fuel injection system precisely controls the air/fuel mixture. The vehicle's ECM maintains the air/fuel mixture at the optimum conditions for minimizing emissions, while maximizing performance. In open loop (during wide open throttle operation) the oxygen sensor doesn’t interfere as much allowing more fuel to be used to develop more power.
The fuel system and catalytic converter must have the proper balance of air and fuel in order to maintain low emissions. The stoichiometric 14.7:1 air/fuel ratio is catalyst efficiency is greatest in uniformly reducing all emissions. The carbon monoxide emissions will be lower at a fuel mixture leaner than 14.7:1, but a sacrifice is made with an increase in hydrocarbons and oxides of nitrogen. Once again, this is all done while cycling the air fuel ratio from a lean to rich condition to maintain catalyst temperature.
The fuel control program managed by the ECM maintains an average air/fuel ratio of 14.7:1 for optimum catalyst efficiency. This balance is difficult to maintain because of the changing variables such as RPM and engine load. To maintain balance, the ECM forces the system rich for approximately 300 milliseconds and then forces the system lean for the same amount of time. The longer the system stays rich the longer it stays lean. The system is correcting for a lean condition and is still considered in "closed loop" operation. The electronic feedback carburetor fuel systems of this era were only capable of making approximately 10 changes in a second.
The Clean Air Act Amendments of 1990 recognized the fact that vehicles with malfunctioning emissions control systems could go undetected for extended periods. Annual emissions inspection programs were not enough. The EPA required vehicle manufacturers to produce vehicle onboard diagnostic systems (OBD) capable of immediately identifying the driver of emissions faults effective from 1996. As part of the OBD II system, all emissions-related components would be monitored for malfunction or deterioration.
On today's new vehicles, HC and CO emissions are reduced by more than 95% when compared to a 1960's vintage vehicle; NOx emissions are reduced by 90%.
The exhaust emissions of automotive engines contain a number of harmful pollutants. In order to minimize the amount of harmful pollutants being produced, manufacturers have developed automotive emissions controls. The following is a list of the harmful exhaust gases manufacturers are obligated to reduce, which includes how the gases are formed and why they are dangerous.
Carbon Monoxide (CO)
Consists of equal parts of carbon & oxygen. This colorless, odorless, poisonous gas is the product of incomplete combustion. Incomplete combustion increases hydrocarbon levels and also increases CO. By weight, carbon monoxide accounts for 47% of air pollution.
Hydrocarbon (HC)
Hydrocarbons consist of carbon and hydrogen. All petroleum-based fuels contain hydrocarbons. Hydrocarbons are emitted from two areas of a vehicle. This first is the tailpipe and the second is from the fuel system, commonly known as evaporative emissions. Early emissions controlled vehicles had vented gas tanks. That allowed fuel vapor to enter the atmosphere. Additionally, carburetor float bowls were vented to atmosphere. Today’s OBD-2 vehicles have an elaborate EVAP system that controls fuel vapor and directs it back into the fuel tank during normal operation. When the engine is OFF, the EVAP system shuts down to prevent fuel vapor from entering the atmosphere. Additionally, during smog or emission inspections the gas cap is routinely checked to ensure the seal has not become compromised. Hydrocarbons are one of the key elements responsible for the production of photochemical smog.
Oxides of Nitrogen (NOx)
Oxides of nitrogen consist of nitrogen combined with various amounts of oxygen. Oxides of nitrogen are formed when nitrogen binds with oxygen in the presence of the heat developed during the combustion process. Oxides of nitrogen are also a main component in smog.
Photochemical Smog
Photochemical smog, commonly referred to simply as smog, and is a by-product of the combination of HC and NOx. In the presence of sunlight these two elements form ozone (O3), nitrogen dioxide, and nitrogen nitrate; all of which cause respiratory problems. Nitrogen dioxide is a light brown colored gas which can affect visibility in air corridors around major airport terminals and above highways. Auto manufacturers’ are committed to reducing HC, CO, and NOx emissions that all contribute to photochemical smog.
Particulates
Particulates are tiny particles of solids that are dispersed into the atmosphere during any burning process. Particulates are composed of carbon, ash, oil, grease, and metal oxides. Smoke, haze, and dust are types of air pollution which are readily visible and are known to complicate respiratory problems cause by smog.