A current CRC project is examining the relationship between vehicle performance and octane rating. The "Sub-Regular Grade Octane Rating (85AKI) Study" (Project # E-108) should reveal the effect of octane rating on greenhouse gases, emissions and other performance indicators.
The relationship between these parameters is not straightforward. For instance, a higher octane rated fuel may contain more aromatics, which can raise emissions. On the other hand, modern pollution control equipment should make this unimportant because the emission control technology cleans up a vehicle's exhaust. Likewise, anti-knock technology largely prevents knocking, even if a fuel's octane rating is slightly below specification.
When it comes to fuel octane rating, the U.S. has two regions. One is at or near sea-level. The second is at altitude. In this second area, the octane rating of the fuel is typically lower by two points or so as compared to that at sea level.
Bill Studzinski, a GM Powertrain fuels technical specialist, is a member of the CRC Performance Committee, which is coordinating the study. A member of the Society of Automotive Engineers (SAE), ASTM and the National Council of Weights and Measures, Studzinski answered questions from ACFA about the study and its implications.
Q: What are the goals and structure of the study? What do you hope to accomplish?
Studzinski: The study objective is to understand the vehicle performance, tailpipe emissions, and fuel economy effects of operating a fleet of modern, computer controlled U.S. vehicles on two matched test fuels that differ only in octane rating; 87 and 85 Anti-knock Index (AKI). This testing will be done at two elevations, 1,000 and 5,000 feet (300 to 1500 m), to understand the influence of altitude on these vehicle performance results.
Q: How interested are OEMs in this study? Has this interest been increasing? If so, what indicates this increase and why do you think that is?
Studzinski: GM can only answer on its own behalf and can tell you that we are very interested in this study in order to develop quantitative data, collected in a very controlled manner, to help understand market fuel quality effects on vehicle performance. The interest in the study has been growing because a gasoline's octane rating plays a critical role in a vehicle's fuel economy, emissions, and performance.
Q: When do you expect testing to finish? When will reports be completed?
Studzinski: Testing should be finished by the end of 2013 and reports written in 1st quarter of 2014.
Q: What performance parameters are being studied? What was the thinking behind picking these?
Studzinski: Vehicle tailpipe emissions, fuel economy and performance parameters such as engine speed, manifold absolute pressure, percent engine load, ignition timing, fuel equivalence ratio and exhaust system temperatures will be measured during specified US emissions test cycles. These cycles were chosen because they are automotive industry standard emissions cycles, provide repeatable vehicle speed duty cycles for ease in comparing fuel effects and very generally represent mild to severe consumer driving behaviors.
Q: What different altitudes and octane ratings are being looked at? Why were these chosen?
Studzinski: The two test elevations for the program are 1,000 ft. and 5,000 ft. They were chosen to help understand fuel effects on vehicles in the Rocky Mountain States compared to the majority of U.S. drivers, which are at a much lower elevation.
Q: There has been talk about well-to-wheels evaluation of octane rating. In this, the energy cost of refining a higher octane fuel would be balanced against the higher fuel efficiency made possible by such a fuel. How does this study fit into these calculations and this debate?
Studzinski: As I see it, this study does not fit directly into a well-to-wheels (WTW) analysis of U.S. gasoline octane ratings. For example, the vehicle piece (tank-to-wheel piece) of a WTW analysis would require detailed engine dynamometer studies with "open architecture" engine computer controls and prototype engine parts where you could measure optimal engine efficiency from a variety of fuels and conditions. Additional engine effects like specific fuel consumption, combustion phasing and in-cylinder pressures would be needed to understand the big picture of fuel effects on performance. By contrast, this CRC octane program uses production vehicles, with "fixed" engine controls and architectures, and measures only the effects of two octane levels on specific performance attributes.
Q: At present, the U.S. – and ASTM, for that matter – does not specify a minimum octane rating. What role can – or should – this study play in the debate surrounding this?
Studzinski: The predominant gasoline quality specification in the U.S. is ASTM D4814, "Standard Specification for Automotive Spark-Ignition Engine Fuel." It currently does not specify minimum octane rating levels but rather includes an Appendix on pertinent information but is not mandatory. This CRC study, like all CRC studies, provides technical data from which the ASTM voting members can choose to consider while creating test methods and specifications. The hope is that ASTM members consider this data very helpful, accurate and without bias.
Q: Where do you see things headed in the future? Do you expect more of this type of performance evaluation with respect to octane and other fuel parameters? What would that buy?
Studzinski: I do see more studies on octane rating effects on vehicle performance being conducted because it's the number one fuel parameter affecting engine and vehicle performance. Each of the industries, automotive and fuel production, is working to minimize GHG emissions and needs to understand gasoline octane rating's effects.
Q: Is there anything else you'd like to add or feel should have been mentioned that wasn't?
Studzinski: I am as eager as the rest to see the results of this program!