Onboard refueling vapor recovery
An Onboard refueling vapor recovery system (ORVR) is a vehicle fuel vapor emission control system that captures volatile organic compounds (VOC, potentially harmful vapors) during refueling.[page needed] There are two types of vehicle emission control systems: the ORVR, and the Stage II vapor recovery system. Without either of these two systems, fuel vapors trapped inside gas tanks would be released into the atmosphere, each time refueling of the vehicle occurred. However, an ORVR system is able to retain those emissions, delivering them to the vehicle's activated carbon-filled canister and then to dispose of those vapors by adding them to the engine's inlet manifold and the stream of fuel supplying the engine, during normal operation. The goal behind implementing the ORVR system throughout the U.S. is to eventually make the Stage II systems obsolete.
According to Freda Fung and Bob Maxwell, the Environmental Protection Agency (EPA) has been controlling emissions among the United States since the 1970s. They implemented regulations which would limit the amount of fuel vapor released into the atmosphere during the refueling of a motor vehicle. Before any EPA mandate was put into action, California devised its own regulations, ahead of every other state, by 16 years, when it required the implementation of the Stage II vapor recovery system. The ORVR systems were required but did not take over instantaneously; instead, EPA decided that Stage II control systems were necessary for all areas of non attainment (an area considered to have air quality worse than the National Ambient Air Quality Standards as defined in the Clean Air Act Amendments of 1970) until the requirement had been dropped by the Clean Air Act of 1990. In the United States, ORVR has been mandated on all passenger cars (phasing in over the 1998-2000 model years) and light trucks up to 10,000 lbs gross vehicle weight rating (phasing in over the 2001-2006 model years) by the EPA.
As the years went by, ORVR systems became so widespread throughout the United States, that Stage II systems were becoming obsolete. On May 9, 2012 EPA Administrators released their final rule making which acknowledged enough ORVR systems were operational to remove further need for Stage II systems. However, it left the option open to those states that felt the use of Stage II was still necessary for their particular area.
- According to EPA, ORVR vehicles function at 98% efficiency, while the efficiency of the Stage II system ranges from 62% to 92%.
- The ORVR system is significantly less expensive than the Stage II system.
- The lifespan and durability of the ORVR system is much greater than the Stage II System. That translates into much lower maintenance costs for the ORVR system.
- The Stage II system cannot collect diurnal emissions, while the ORVR system can.
Complications between ORVR & Stage II
Vehicle ORVR systems have design characteristics that are not compatible with Stage II vacuum assisted systems. When these two systems work in conjunction, the overall efficiency declines significantly, as compared to each system functioning on its own.
An ORVR carbon-filled canister (installed on modern vehicles) is designed to capture fuel vapors displaced while refueling, and then to inject them into the intake manifold later on, so that they are burned along with the regular fuel, during normal engine operation. However, a Stage II vapor recovery system, installed on refueling gas station pumps, uses a vacuum to prevent fuel vapors from being released into the atmosphere. The design of the fill pipe seal in ORVR systems, prevents fuel vapors from entering the fuel tank fill pipe. That frustrates the purpose of the Stage II nozzle, which was designed to vacuum away any fuel vapors that come up that fill pipe, during the refuelling process. If the car's own vapor recovery system is working properly, then the Stage II nozzle will only be vacuuming normal fresh air and depositing that into the gas station's underground fuel storage tanks. That ends up causing evaporation of fuel vapors into the atmosphere, because too much pressure builds up in those fuel storage tanks. When that pressure becomes too great, it is released into the atmosphere via a pressure relief pipe.
The vapors which are displaced from the fuel tank by the incoming fuel are routed via the vapor vent line to the canister and are absorbed by activated carbon. These canisters are fabricated from either steel or plastic. The size of this canister is tailored to accommodate expected evaporative emissions. The emissions occur diurnally or throughout the day, even when the vehicle is parked.
Fuel tank filler pipe with seal (liquid or mechanical )
A mechanical seal would most likely be created out of an annular elastomeric material through which the nozzle must pass during refueling, preventing vapors from escaping alongside the nozzle. A liquid seal is created by the design of the filler pipe, which creates a seal with the liquid flowing into the tank. Since the liquid fills the entire pipe, no emissions can escape during refueling. A liquid seal is usually used for smaller vehicles, while the mechanical seal is used for larger vehicles.
It is designed to open the purge vent line, between the canister and the engine, to enable manifold vacuum to pull air through the canister and purge it of fuel vapors. The electronic control unit (ECU) controls the opening and closing of this valve.[dead link]
Vent/purge vapor lines
It provides a method of controlled escape for gasoline vapors during the refueling process. It has a mechanism which closes the vent in the event the vehicle rolls over, to prevent spilling of VOCs or fuel in general. It also acts as a fill limiter.[dead link]
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- On board refueling vapor recovery system, retrieved 2015-11-09
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- "Federal Register | Air Quality: Widespread Use for Onboard Refueling Vapor Recovery and Stage II Waiver". www.federalregister.gov. Retrieved 2015-10-27.
- Cincinnati, OARM. "Useful sites in addition to NSCEP". Archived from the original on March 11, 2016. Retrieved 2015-10-27.