- Research Field -
A. Miyoshi
Chemical Kinetics
Our research field is called
Chemical Kinetics of
free radicals.
For example, the catalytic
behavior of the following ozone destruction reaction by chlorine atoms
[1]
(See the page of
Free Radicals,
for details),
that one chlorine atom desroys 10
4 ozone molecules,
cannot be explained either by the net reaction nor by the reaction (1)
or (2) only.
| Cl + O3 → ClO + O2 | (1) |
| ClO + O → Cl + O2 | (2) |
| O + O3 → 2 O2 (net reaction) |
The purpose of our research is to elucidate what reactions
[reactions (1) and (2) in the example shown above] are involved
in the target phenomenon [the ozone destruction, here].
Obviously, for the atmospheric environmental problems, the accurate
understanding of the phenomena is required to discuss the
countermeasures.
Also, the knowledge on the chemical kinetics of the combustion is
inevitable for the development of highly efficient and low-emission
combustion technologies and assessment of the combustion or explosion
safely.
Below are the three major elementary reactions involved in the
high-temperature combustion of hydrogen, which is the chamically simplest
fuel.
| H + O2 → OH + O | (3) |
| O + H2 → OH + H | (4) |
| OH + H2 → H2O + H | (5) |
| 2H2 + O2 → H2O + H + OH (net reaction??) |
Contrary to the ozone destruction chain reaction, for which the chain
carriers (chemical species that carry the chain reaction; Cl and ClO for
the ozone destruction) disappear in the net reaction since their
consumption and production is in balance, chain carriers (H, O, and OH)
always remains in the right hand side of the net reaction irrespective
of the ways of the summation for this chain reaction system of hydrogen.
This is because the reactions (3) or (4) produces two chain
carriers from one chain carrier.
Such a chain reaction system is called branching chain reaction
system, and it describes the essense of the explosive nature of the
mixture of fuel
such as hydrogen and oxygen (or air) that it results in the explosion
with a small triggering by self-multiplication of the chain carriers.
For the combusion of hydrogen, it is possible to describe the
combsution and explotion phenomena with totally 20 elementary steps
includeing the three shown above.
However, for hydrocarbon molecules with large number of carbons,
a huge number of elementary steps are necessary to describe the combustion
phenomena; for example, to describe the combustion of heptane
(C
7H
16), thousands of elementary reactions are
needed.
The goal of one of our research projects is the construction of
reliable reaction mechanisms for such huge reaction systems, via the
development of a software tool which automatically estimates the
reaction mechanisms and technique to find systematic change of the
rate coefficients by the quantum chemical calculations.
Current Research Subjects
A few of our current research subjects are introduced below.
The reduction of the particulate matter (soot)
and polycyclic aromatic hydrocarbons (PAH) emitted from the internal
combustion engines is one of the important missions for the combustion
technology.
However, the chemical process of soot formation
is very complicated, and our knowledge on it is far from
the predictable modeling and thus the development of combustion technology
still relies largely on the empirical knowledge.
Experimental measurements and quantum chemical calculations
for key reactions are under way and our final
goal is to establish a reliable chemical reaction model.
Low-Temperature Oxidation Mechanism of
Hydrocarbons
The dominant combustion oxidation process of hydrocarbon below
about 900 K is called 'low-temperature oxidation process,' which
is important to understand the ignition phenomena of fuel/air
mixtures.
The knowledge on the process is required since it
controls the 'knocking' in spark ignition engines, as well as
to control and understand the HCCI combustion.
Our main purpose is to understand the mechanism of the reactions
in the process, which include complex isomerization reactions of
radicals by experimantal direct investigations of hydrocarbon radicals
and peroxy radicals and quantum chemical calculations.
Construction of the Mechanism for New-Types
of Oxidants
Although, in recent semiconductor industry, use of the new
types of oxidant gases (NF3, ClF3, ClF5,
etc.) for etching and cleaning are increasing, the combustion safety
regulations for this gases when they are made contact with hydrocarbons
have not been well standarized.
We are constructing the reaction mechanisms for these new types
of oxidant with hydrocarbons by using the quantum chemical calculations.
