Biomedical subjects

M Matti Maricq

Publications and source records attributed to M Matti Maricq.

5 recordsLinked to original sources

PubMed2005

Dimethyl ether oxidation at elevated temperatures (295-600 K).

Dimethyl ether (DME) has been proposed for use as an alternative fuel or additive in diesel engines and as a potential fuel in solid oxide fuel cells. The oxidation chemistry of DME is a key element in understanding its role in these applications. The reaction between methoxymethyl radicals and O(2) has been examined over the temperature range 295-600 K and at pressures of 20-200 Torr. This reaction has two product pathways. The first produces methoxymethyl peroxy radicals, while the second produces OH radicals and formaldehyde molecules. Real-time kinetic measurements are made by transient infrared spectroscopy to monitor the yield of three main products-formaldehyde, methyl formate, and formic acid-to determine the branching ratio for the CH(3)OCH(2) + O(2) reaction pathways. The temperature and pressure dependence of this reaction is described by a Lindemann and Arrhenius mechanism. The branching ratio is described by f = 1/(1 + A(T)[M]), where A(T) = (1.6(+2.4)(-1.0) x 10(-20)) exp((1800 +/- 400)/T) cm(3) molecule(-1). The temperature dependent rate constant of the methoxymethyl peroxy radical self-reaction is calculated from the kinetics of the formaldehyde and methyl formate product yields, k(4) = (3.0 +/- 2.1) x 10(-13) exp((700 +/- 250)/T) cm(3) molecule(-1) s(-1). The experimental and kinetics modeling results support a strong preference for the thermal decomposition of alkoxy radicals versus their reaction with O(2) under our laboratory conditions. These characteristics of DME oxidation with respect to temperature and pressure might provide insight into optimizing solid oxide fuel cell operating conditions with DME in the presence of O(2) to maximize power outputs.

Journal Article↗

PubMed2003

Airborne brake wear debris: size distributions, composition, and a comparison of dynamometer and vehicle tests.

Particle size distributions of light-duty vehicle brake wear debris are reported with careful attention paid to avoid sampling biases. Electrical low-pressure impactor and micro-orifice uniform deposit impactor measurements yield consistent size distributions, and the net particulate matter mass from each method is in good agreement with gravimetric filter measurements. The mass mean diameter of wear debris from braking events representative of urban driving is 6 microm, and the number-weighted mean is 1-2 microm for three currently used classes of lining materials: low metallic, semimetallic, and non-asbestos organic (NAO). In contrast, the wear rates are very material dependent, both in number and mass of particles, with 3-4 times higher emissions observed from the low metallic linings as compared to the semimetallic and NAO linings. Wind tunnel and test track measurements demonstrate the appearance of micron size particles that correlate with braking events, with approximately 50% of the wear debris being airborne for the test vehicle in this study. Elemental analysis of the wear debris reveals a consistent presence of the elements Fe, Cu, and Ba in both dynamometer and test track samples.

Air Pollutants↗

PubMed2003

A constant-volume rapid exhaust dilution system for motor vehicle particulate matter number and mass measurements.

An improved version of the constant volume sampling (CVS) methodology that overcomes a number of obstacles that exist with the current CVS dilution tunnel system used in most diesel and gasoline vehicle emissions test facilities is presented. The key feature of the new sampling system is the introduction of dilution air immediately at the vehicle tailpipe. In the present implementation, this is done concentrically through a cylindrical air filter. Elimination of the transfer hose conventionally used to connect the tailpipe to the dilution tunnel significantly reduces the hydrocarbon and particulate matter (PM) storage release artifacts that can lead to wildly incorrect particle number counts and to erroneous filter-collected PM mass. It provides accurate representations of particle size distributions for diesel vehicles by avoiding the particle coagulation that occurs in the transfer hose. Furthermore, it removes the variable delay time that otherwise exists between the time that emissions exit the tailpipe and when they are detected in the dilution tunnel. The performance of the improved CVS system is examined with respect to diesel, gasoline, and compressed natural gas vehicles.

Air Pollutants↗

PubMed2002

The effects of the catalytic converter and fuel sulfur level on motor vehicle particulate matter emissions: gasoline vehicles.

Scanning mobility and electrical low-pressure impactor particle size measurements conducted during chassis dynamometer testing reveal that neither the catalytic converter nor the fuel sulfur content has a significant effect on gasoline vehicle tailpipe particulate matter (PM) emissions. For current technology, port fuel injection, gasoline engines, particle number emissions are < or = 2 times higher from vehicles equipped with blank monoliths as compared to active catalysts, insignificant in contrast to the 90+% removal of hydrocarbons. PM mass emission rates derived from the size distributions are equal within the experimental uncertainty of 50-100%. Gravimetric measurements exhibit a 3-10-fold PM mass increase when the active catalyst is omitted, which is attributed to gaseous hydrocarbons adsorbing onto the filter medium. Both particle number and gravimetric measurements show that gasoline vehicle tailpipe PM emissions are independent (within 2 mg/mi) of fuel sulfur content over the 30-990 ppm concentration range. Nuclei mode sulfate aerosol is not observed in either test cell measurements or during wind tunnel testing. For three-way catalyst equipped vehicles, the principal sulfur emission is SO2; however a sulfur balance is not obtained over the drive cycle. Instead, sulfur is stored on the catalyst during moderate driving and then partially removed during high speed/load operation.

Air Pollutants↗

PubMed2002

The effects of the catalytic converter and fuel sulfur level on motor vehicle particulate matter emissions: light duty diesel vehicles.

Wind tunnel measurements and direct tailpipe particulate matter (PM) sampling are utilized to examine how the combination of oxidation catalyst and fuel sulfur content affects the nature and quantity of PM emissions from the exhaust of a light duty diesel truck. When low sulfur fuel (4 ppm) is used, or when high sulfur (350 ppm)fuel is employed without an active catalyst present, a single log-normal distribution of exhaust particles is observed with a number mean diameter in the range of 70-83 nm. In the absence of the oxidation catalyst, the high sulfur level has at most a modest effect on particle emissions (<50%) and a minor effect on particle size (<5%). In combination with the active oxidation catalyst tested, high sulfur fuel can lead to a second, nanoparticle, mode, which appears at approximately 20 nm during high speed operation (70 mph), but is not present at low speed (40 mph). A thermodenuder significantly reduces the nanoparticle mode when set to temperatures above approximately 200 degrees C, suggesting that these particles are semivolatile in nature. Because they are observed only when the catalyst is present and the sulfur level is high, this mode likely originates from the nucleation of sulfates formed over the catalyst, although the composition may also include hydrocarbons.

Air Pollutants↗