SISGR: Dynamics of Radical Reactions in Biodiesel Combustion

Recipient Organization
STATE UNIV OF NEW YORK
(N/A)
SYRACUSE,NY 13210

Performing Department
Chemistry

Non Technical Summary
The ignition of diesel fuel depends on isomerization of peroxy radicals (ROO•) via ahydrogen shift reaction:ROO• ---+ QOOH (1)where QOOH represents a carbon-centered hydroperoxy radical product, e.g., for R= ethyl:CH3CH200• l,4H-shift > •CH2CH200H (1a)Production of multiple OH radicals in the chemistry following reaction (1) leads to autoignition.Figure 1, below, illustrates the pathways competing with formation of •CH2CH200H and thecompeting fates of •CH2CH200H, itself. The fate of CH3CH200• depends not only on howtemperature and pressure affects the semiclassical rate constants, but also on the extent ofquantum mechanical tunneling and chemically activated processes.Experimentalists face several difficulties in gaining an understanding of this chemistry, andno QOOH species has ever been detected by experiment! This has inspired many computationalstudies of these processes. A major deficit of these computational efforts has been the limitedaccuracy of the treatment of lUnneling and the neglect of variational effects: only onedimensionaltreatments of tunneling have been used and variational effects have been neglected.Given the expected importance of tunneling in these reactions at the low temperatures importantfor diesel ignition, and ubiquity of large variational effects, much more accurate theoreticaltreatments are required. Another limitation is that the peroxy radicals studied to date have beenalmost exclusively those derived from alkanes.

Animal Health Component

(N/A)

Research Effort Categories

Basic

100%

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
402	5399	2000	100%

Knowledge Area
402 - Engineering Systems and Equipment;

Subject Of Investigation
5399 - Structures, facilities, and equipment, general/other;

Field Of Science
2000 - Chemistry;

Keywords

diesel fuel

auto ignition

peroxy radical

Goals / Objectives
The goal of this research is to gain fundamental insights into the dynamics of 1 ,n H -shiftreactions of peroxy radicals and the competing H02 elimination reaction that:• include effects of functional groups (e.g., ester or olefin)• include rigorous treatments of tunneling, non-classical reflection, and variational effects• quantify the effect of chemically activated processes• synthesize the results into structure-activity relations (SARs)

Project Methods
We will use state of the art methods of computational chemistry to investigate reactions that arerelevant to the critical intermediates involved in diesel combustion. Quantum chemistry will be used to study the effects of functionalgroups on the heights and widths of reaction barriers, focusing on ROO• containing the ester andolefin groups that are of interest to biodiesel combustion. Variational transition state theory willbe used to determine how the position of the dynamical transition state differs from that of thesaddle point, and to calculate semi-classical rate constants for the reactions of interest.Multidimensional tunneling calculations will be carried out to investigate the effects of tunneling. and non-classical reflection on rate constants; comparisons will be made of the relative importance of small-curvature versus large-curvature tunneling paths. RRKM/Master Equation calculations will be used to determine the extent of chemically activated versus thermal reactions on these complicated potential energy surfaces, which will enable comparisons to experimental yields of stable and radical products.

Progress 09/28/15 to 09/30/15

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?A postdoc, two graduate students, and two undergraduate students received training in using high-performance computing resources, quantum chemistry, theoretical kinetics, and applications of these tools to problems in combustion chemistry. All five trainees received training in presenting scientific results orally and in writing. The postdoc and two graduate students got to present their work at multiple scientific conferences, which are important opportunities for professional development. The post-doc is now and associate professor, and the graduate student who is not still in graduate school obtained a position in industry related to diesel combustion. How have the results been disseminated to communities of interest?Results have been disseminate through publication of four scientific papers in peer-reviewed journals. In addition, six talks and four posters have been presented at national or international scientific meetings. What do you plan to do during the next reporting period to accomplish the goals?One additional paper is almost ready for submission, and progress is being made on additional quantum chemical and kinetic studies of chemical reactions of interest in biodiesel ignition.

Impacts
What was accomplished under these goals? We obtained fundamental insights into the effects of olefin and ester groups on the dynamics of 1,n H-shift reactions and competing reactions of first and second generation peroxy radicals formed in combustion. We obtained structure-reactivity relationships that are used in models of combustion chemistry. We found that variational effects were modest for these reactions, but that tunneling could be significant at the relatively low (for combustion) temperatures relevant to these reactions in diesel ignition. We also found that a relatively simple approximation could account fairly reliably for tunneling, at least in the high-pressure limit. We found that chemically activated processes could be of importance, especially for the (E)-(Z) transformation of allylic radicals.

Publications