Vehicle evaporative control system

The two liter carbon canister does not exhibit the HC release during the run loss portion of the test, nor does it release more than the allowable level of HC during the three day diumals. Thus, for the given vehicle configuration and the level of purge volume obtained by the vehicle, it is clear that a two liter carbon canister is required for this vehicle to pass the EPA certification requirement. This conclusion has an effect on the cost of the evaporative control system, in that the additional activated carbon volume and canister size will have an added cost, as will any additional hardware required to mount the larger canister on the vehicle. 

On-Board Diagnostics. State of California regulations require that vehicle engines and exhaust emission control systems be monitored by an on-board system to assure continued functional performance. The program is called OBD-II, and requires that engine misfire, the catalytic converter, and the evaporative emission control system be monitored (101). The U.S. EPA is expected to adopt a similar regulation. 

During vehicle operations similar to those experienced during the three day diurnal evaporative test outlined in Fig. 1, the following operations occur in the evaporative emission control system ... 

Fuel system components involved in the refueling process include the fuel tank, filler pipe, filler cap, vapor control valve, liquid-vapor discriminator (LVD) valve, and the carbon canister [27,28]. During vehicle refueling, which is monitored during the integrated refueling test as outlined in Fig. 1, the following operations occur in the evaporative emission control system ... 

The use of activated carbon canisters in the control of running loss evaporative emissions will be presented through the use of an example vehicle application. In this example, the vehicle to be studied is a representative standard size sedan equipped with a 3.0 liter, V6 engine and a 72 liter (18 gallon) fuel tank. The vehicle is assumed to have an evaporative emission control system similar to the one presented in Section 3. 

Applications of activated carbons are discussed in Chapters 8-10, including their use in the automotive arena as evaporative loss emission traps (Chapter 8), and in vehicle natural gas storage tanks (Chapter 9). The use of evaporative loss emission traps has been federally mandated in the U.S. and Europe. Consequently, a significant effort has been expended to develop a carbon adsorbent properly optimized for evaporative loss control, and to design the on board vapor collection and disposal system. The manufacture of activated carbons, and their preferred characteristics for fuel emissions control are discussed in Chapter 8, along with the essential features of a vehicle evaporative loss emission control system. 

The generation of arr pollutants, including VOC s, from automotive vehicles was identified to come from two principal sources vehicle exhaust emissions, and fuel system evaporative emissions [4], Evaporative emissions are defined as the automotive fuel vapors generated and released from the vehicle s fuel system due to the interactions of the specific fuel in use, the fuel system characteristics, and environmental factors. The sources of the evaporative emissions are discussed below and, as presented m the remainder of this chapter, control of these evaporative emissions are the focus of the application of activated carbon technology in automotive systems. 

A current vehicle fuel system designed for evaporative emission control should address enhanced SHED, running loss, and ORVR emission level requirements (see Table 1). A typical vehicle fuel system is shown in Fig. 4. The primary functions of the system are to store the liquid and vapor phases of the fuel with acceptable loss levels, and to pump liquid fuel to the engine for vehicle operation. The operation of the various components in the fuel system, and how they work to minimize evaporative losses during both driving and refueling events, is described below. 

Fig. 4. Representative vehicle fuel system with evaporative emission control...

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