The Co-Optima FY19 Year in Review report released by the U.S. Department of Energy (DOE) describes recent accomplishments to improve efficiency while reducing emissions and cost for the entire on-road fleet of combustion-powered vehicles under the Co-Optimization of Fuels & Engines program.
Lawrence Livermore National Laboratory (LLNL) is playing a key role in this research, collaborating with eight other national labs and more than 20 university and industry partners.
After completing a major body of research focused on boosted (or turbocharged) spark-ignition engines, Co-Optima’s Fiscal Year 2019 (FY19) light-duty research and development changed focus onto solutions that switch between multiple engine operating modes to maximize engine efficiency and fuel economy. Following three years with a strong concentration on light-duty vehicles, in FY19 the Co-Optima team made a planned shift to increase research related to trucks.
Livermore contributed modeling expertise to two projects that were highlighted in the report involving a hyper-boosting blendstock for fuels as well as improved prediction of soot emissions via improved kinetic models for polycyclic aromatic hydrocarbons (PAHs).
In the first project, Co-Optima researchers had previously identified prenol as a “hyper-boosting” blendstock, meaning the octane number (the number listed on the pump at a gas station) of prenol-gasoline blends can be higher than that of either prenol alone or the base gasoline by nearly five octane numbers in some cases (i.e., as much as the difference between regular and premium gasoline).
Octane rating is a standard measure of the performance of gasoline. The higher the octane number, the more compression the fuel can withstand before detonating. Such detonations are known as engine knock, which can cause excessive noise and engine damage. Gasolines with higher octane ratings are used in high-performance engines that use higher compression ratios to achieve higher power-to-weight ratios, through improved thermodynamic efficiency. The high octane ratings achievable with the prenol addition make it an attractive biofuel and warranted further investigation of the physical mechanism(s) that lead to the hyperboosting effect.
“Scott Wagnon, a materials scientist at LLNL, developed an accurate chemical kinetic model for prenol so that its chemistry could be simulated in engines to help better understand its combustion behavior in the engine and to interpret results from engine experiments using blends of prenol and gasoline,” said LLNL Co-Optima representative Bill Pitz.
In the second project, LLNL materials scientist Goutham Kukkadapu modeled the formation of polycyclic aromatic hydrocarbons.
PAHs are produced in fuel-rich mixtures during combustion in an engine and are known to be the main contributor to soot. Soot forms most of the particulate emissions generated by diesel engines, but also can be produced by modern, direct-injection spark-ignition engines.
“This PAH model is being linked to a soot model to predict soot emissions from internal combustion engines,” Pitz said. “Such a soot model is needed to predict the effect of new engine designs and fuel formulations on soot emissions, which need to meet regulated limits.”
LLNL engineers also contributed computational expertise and simulation tools to the Co-Optima program. The Zero-RK suite of codes were used by projects featured in the FY19 Year in Review for surrogate fuel formulation, octane number prediction and kinetic model testing and development. Zero-RK is developed by Matthew McNenly, Russell Whitesides and Simon Lapointe, who are members of LLNL’s Computational Engineering Division.
The FY19 Year in Review highlights the year’s most significant Co-Optima R&D accomplishments, with details on findings that straddle light-, medium- and heavy-duty technologies.
Potential benefits of Co-Optima research include significant improvements in vehicle fuel economy and increases in the use of domestically sourced fuel for transportation. It has the potential to create new U.S. jobs and keep energy dollars in the United States, while reducing emissions and costs for consumers and commercial operators at the pump.
Sponsored by DOE’s Vehicle Technologies Office and Bioenergy Technologies Office, Co-Optima partners include Argonne, Idaho, Lawrence Berkeley, Lawrence Livermore, Los Alamos, Oak Ridge, Pacific Northwest and Sandia National Laboratories, as well as the National Renewable Energy Laboratory.