General Motors Corp. (GM) and other automobile makers support the RFG and oxygenated fuels programs as an important part of efforts to reduce urban air pollution.
In fact, beginning with 1989 model-year cars, GM added to its owners manuals statements recommending the use of oxygenates in areas with high ozone and CO levels. And GM recommended RFG specifically, beginning in 1992.
The fact that these fuels can be used in existing vehicles allows the benefits of reformulated and oxygenated gasolines to be effective almost immediately upon implementation, said Gerald Barnes, manager of clean fuels and heavy duty activities for GM.
The use of these gasolines in existing cars is possible because of continual evolution in vehicle design. But refiners share in this success because, as Barnes points out, motor vehicle fuels have been reformulated almost constantly since automobiles were invented.
Vehicle design changes
Major vehicle changes in recent years include:
- On-board diagnostic systems
The development of on-board computers and exhaust-gas oxygen sensors allowed fuel metering to progress from carburetors to single-point fuel injectors to multi-point, sequential-port fuel injection systems, said Barnes. Recent improvements in these systems have resulted in what are called OBD-II systems. OBD-II designs minimize emissions caused by malfunctions in automobile emission-control systems. These mandated diagnostic systems...are susceptible to more subtle fuel interactions, warns Barnes.
- Fuel system materials
Auto manufacturers have changed fuel system materials substantially to accommodate improvements in vehicle technology and changes in fuels. Upgraded materials have been adopted to withstand oxygenated fuels, says Barnes. These include elastomer and plastic changes, and increased use of stainless steel and other corrosion-resistant components, he added. Also included are epoxy coatings in fuel tanks and decreased-permeation properties of fuel system materials.
RFG issues
Barnes sees reformulated gasoline as having advantages in addition to its emissions-reduction benefits.
Because the reformulated gasoline regulations place some limits on fuel property variation, these gasolines potentially have more uniform properties, leading to reduced variation in vehicle performance and to increased consumer satisfaction, said Barnes.
Some RFG properties, however, are causing concern for automobile makers. These include:
- Reduced volatility
Vapor pressure reductions, if done improperly, can cause poor distillation characteristics, leading to poor driveability, especially in milder cold-weather months. To solve this problem, GM and other manufacturers suggest a driveability index maximum of 1200.
- Reduced sulfur
The automobile industry is concerned about the effects of fuel sulfur on the OBD-II systems of vehicles certified to California low-emission vehicle standards. In Northeastern states, vehicles certified to meet these standards will operate on non-California gasoline.
Test results from the Auto/Oil Air Quality Improvement Research Program indicate that the higher sulfur levels in these gasolines may cause OBD-II systems to illuminate an indicator light, indicating malfunction when none is present.
Barnes says that, in addition to these issues, some problems with fuel cleanliness have occurred during implementation of the RFG program.
In areas where oxygenates have been used for several years, said Barnes, the operating practices required to maintain fuel distribution system cleanliness are well understood. But there may be a learning process required in those areas just beginning to use oxygenates in large volumes.
In addition, says Barnes, contaminants such as chlorides and water have been found in some oxygenate samples, leading to accelerated corrosion of fuel system components. The volatility and cleanliness concerns can be addressed by proper fuel formulation and by good housekeeping practices, he added.
Copyright 1996 Oil & Gas Journal. All Rights Reserved.
