Exhaust CO Emissions Research Articles

Techno-economic comparison between B10 of Eruca sativa L. and other indigenous seed oils in Pakistan

Eruca sativa L. (known as taramira in South Asia) oil biodiesel shows good fuel properties when tested against ASTM D 6751 standard. Environmental performance of taramira oil B10 (10% (v/v) biodiesel blends with mineral diesel fuel, which is based upon the target set by the Government of Pakistan for 2025) in terms of engine exhaust emissions of CO 2, CO, SO 2, NO X and PM 10 is compared with jatropha, castor and canola oil B10 fuels and found to be better. However, its calorific value is low thus resulting in poor engine performance in comparison to other B10 fuels. In addition, due to the high cost of taramira oil at present, it is not economical to produce in comparison to jatropha biodiesel. Study suggested that these drawbacks may be circumvented by growing taramira plants on large scale on marginal lands across South Asian countries and conducting further research to increase its calorific value.

The Use of Rice Bran Oil as a Fuel for a Small Horse-power Diesel Engine

Increasing cost and scarcity of petroleum resources have promoted research in alternative fuels for internal combustion engines. Among various possible options, fuels derived from triglycerides (vegetable oils/animal fats) are promising substitutes of fossil diesel fuels. Vegetable oil poses some problems when subjected to prolonged use in compression ignition engines because of its high viscosity as reported by researchers. In this present research, experiments were designed to study the effect of low viscous rice bran oil on engine's combustion. The viscosity of the oil was reduced by increasing the fuel temperature. A single cylinder, 5 hp, four stroke, constant speed, water cooled, direct injection diesel engine typically used in stationary operation was used for the experiments. The acquired data were analyzed for various parameters, such as thermal efficiency, brake specific fuel consumption, exhaust emission of CO, CO2, HC, and NOx gases. While operating the engine on rice bran oil (preheated and blends), performance was found to be very close to that of mineral diesel for lower blend concentrations. The preheated oil's performance was slightly inferior in efficiency due to low heating value. As for the pollution point of view, it can perform well for the unmodified engine for a long period operation without any ignition problems. People of rural areas can use this for their agricultural engines without modification.

Prediction of performance and emissions of an engine fuelled with natural gas/hydrogen blends

In this work a methodology is presented for studying the influence of the addition of small percentages of hydrogen in spark-ignition engines running on natural gas, on CO and the NOx exhaust emissions. Thermo-chemical models are used to predict the exhaust emissions. The general inputs of these models are the geometry of the combustion chamber, correlations for the laminar burning velocity of the fuels considered and an expression of the flame speed ratio (ratio of turbulent speed to laminar speed). In the present work, the geometry of the combustion chamber and the flame speed ratio of the engine are first estimated from data corresponding to similar engines, since a direct measurement of them was not possible. In a second step, correlations for the burning velocity of natural gas and hydrogen mixtures as a function of the temperature are determined inside a constant volume combustion bomb designed for the study of premixed combustions. In a third step, a quasi-dimensional model is used to predict the thermal parameters evolution and the optimum ignition timing in different conditions, and then a chemical-kinetic model is used to predict the NOx and CO exhaust emissions of the spark-ignition engine by using the results obtained in the previous sections as inputs.

Ship emissions and their externalities for Greece

The existing and emerging international and European policy framework for the reduction of ship exhaust emissions dictates the need to produce reliable national, regional and global inventories in order to monitor emission trends and consequently provide the necessary support for future policy making. Furthermore, the inventories of ship exhaust emissions constitute the basis upon which their external costs are estimated in an attempt to highlight the economic burden they impose upon the society and facilitate the cost–benefit analysis of the proposed emission abatement technologies, operational measures and market-based instruments prior to their implementation. The case of Greece is of particular interest mainly because the dense ship traffic within the Greek seas directly imposes the impact of its exhaust emission pollutants (NO x, SO 2 and PM) upon the highly populated, physically sensitive and culturally precious Greek coastline, as well as upon the land and seas of Greece in general, whereas the contribution of Greece in the global CO 2 inventory at a time of climatic change awareness cannot be ignored. In this context, this paper presents the contribution of Greece in ship exhaust emissions of CO 2, NO x, SO 2 and PM from domestic and international shipping over the last 25 years (1984–2008), utilizing the fuel-based (fuel sales) emission methodology. Furthermore, the ship exhaust emissions generated within the Greek seas and their externalities are estimated for the year 2008, through utilizing the fuel-based (fuel sales) approach for domestic shipping and the activity-based (ship traffic) approach for international shipping. On this basis, it was found that during the 1984 to 2008 period the fuel-based (fuel sales) ship emission inventory for Greece increased at an average annual rate of 2.85%. In 2008, the CO 2, NO x, SO 2 and PM emissions reached 12.9 million tons (of which 12.4 million tons of CO 2) and their externalities were found to be around 3.1 billion euro. With regard to shipping within the Greek seas, the utilization of the fuel-based (fuel sales) analysis for domestic shipping and the activity-based (ship traffic) analysis for international shipping shows that the ship-generated emissions reached 7.4 million tons (of which 7 million tons of CO 2) and their externalities were estimated at 2.95 billion euro. Finally, the internalization of external costs for domestic shipping was found to produce an increase of 12.96 and 2.71 euro per passenger and transported ton, respectively.

Application of Artificial Neural Networks for Emission Modelling of Biodiesels for a C.I Engine under Varying Operating Conditions

The technical analysis conducted in this study deals with the modelling of diesel engine exhaust emissions using artificial neural networks. Objective of this study is to understand the effectiveness of various biodiesel fuel properties and engine operating conditions on diesel engine combustion towards the formation of exhaust emissions. The experimental investigations have been carried out on a single cylinder Direct Injection (DI) combustion ignition (CI) engine using blends of biodiesel methyl esters from Pongamia, Jatropha and Neem oils. The performance parameters such as brake power (BP), brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), volumetric efficiency, exhaust gas temperature (EGT) were measured along with regulated and unregulated exhaust emissions of CO, HC and NOx. An Artificial neural network (ANN) was developed based on the available experimental data. Multi layer perceptron neural network was used for nonlinear mapping between input and output parameters of ANN. Biodiesel blend percentage, calorific value, density, Cetane number of each biodiesel blend and operating load were used as inputs to train the neural network. The exhaust gas emissions - NOx, CO and HC are predicted for the new fuel and its blends. Different activation functions and several rules were used to train and validate the normalized data pattern and an acceptable percentage error was achieved by Levenberg-Marquardt design optimization algorithm. The results showed that training through back propagation was sufficient enough in predicting the engine emissions. It was found that R (Regression Coefficient) values were 0.99, 0.95 and 0.99 for NOx, CO and HC emissions, respectively. Therefore, the developed model can be used as a diagnostic tool for estimating the emissions of biodiesels and their blends under varying operating conditions.

Emissions from Using Viscous Agent-Treated Fishing Boat Fuel Oil: Tests with a Heavy-Duty Diesel Engine (HDDE) Dynamometer

In order to clamp down on the illegal use of fishing boat fuel A (FBFA) and to reduce exhaust emissions in Taiwan, the residue from a desulfurization unit (RDS) and pyrolysis fuel oil (PFO) were added into FBFA with the ratio of 0.5% to form two new blended fuels (RDS0.5 and PFO0.5). The appearances of fuels from dark to light are RDS0.5, PFO0.5, and FBFA. The two new fuels have higher viscosity than FBFA, which may damage engines and reduce the misuse. The exhaust emissions of CO, HC, NOx, polycyclic aromatic hydrocarbons (PAHs), and carcinogenic potencies (BaPeq) were analyzed by the heavy duty diesel engine (HDDE) transient cycle test. The results show that RDS0.5 has significantly lower particulate matter (PM) emissions, while the PM emissions of PFO0.5 are higher than those of FBFA. In addition, the total PAHs emissions concentration of all three of fishing boat fuels increase from premium (regular) diesel fuel. However, RDS0.5 has relatively lower BaPeq emissions, which are usually considered as carcinogens, than the other fishing boat fuel.

English

Experiments were conducted to control the exhaust emissions from two-stroke, single cylinder, spark ignition (SI) engine, with alcohol blended gasoline (90% gasoline, 10% ethanol by volume) having copper coated combustion chamber [CCCC, copper-(thickness, 300 μ) coated on piston crown, inner side of cylinder head] provided with catalytic converter with sponge iron as catalyst and compared with conventional SI engine (CE) with pure gasoline operation. Aldehydes were measured by wet chemical method. Exhaust emissions of CO and UBHC were evaluated at different values of brake effective pressure, while aldehydes were measured at full load operation of the engine. A microprocessor-based analyzer was used for the measurement of CO/UBHC in the exhaust of the engine. Copper coated combustion chamber with alcohol blended gasoline considerably reduced pollutants in comparison with CE with pure gasoline operation. Catalytic converter with air injection significantly reduced pollutants with test fuels on both configurations of the engine. The catalyst, sponge reduced the pollutants effectively with both test fuels in both versions of the engine.

Application of semi-direct injection for spark-ignition engine

This paper proposes an application of a motorcycle engine lean-burn system for improving engine efficiency and reducing exhaust emissions. This Semi-Direct Injection (SDI) system consists of a high swirl charge, injection during intake-valve opening, and air-assisted fuel injection. The fuel enters the cylinder directly through the intake valve near the middle intake stroke for a richer mixture around the spark plug. A 125 cc, 4-valve, Port-Fuel-Injection (PFI) engine was retrofitted by designing a control plate to enhance the swirl. The swirl ratio was increased to 3.8 and the lean limit was extended to 1.7 of lambda (excess air ratio). The engine was tested at the low-load region, which includes most operation points of the ECE-40 driving cycle. A complete engine performance map was conducted for comparison between SDI and original PFI engines. The results show that Brake-Specific Fuel Consumption (BSFC) decreased by 11.3%. Brake-specific exhaust emissions of NOx and CO decreased by 32.0% and 92.9%, respectively. The HC emission increased by 47.7%.

The effect of adding dimethyl carbonate (DMC) and ethanol to unleaded gasoline on exhaust emission

Oxygen containing additives are usually used to improve gasoline’s performance and reduce exhaust emissions. In this study, the effect of oxygen containing additives on gasoline blended fuels on exhaust emissions was investigated for different engine speeds in a single cylinder, four-stroke, spark-ignition engine. The results indicate that CO and HC exhaust emissions are lower with the use of ethanol–gasoline and DMC–gasoline blended fuels as compared to the use of unleaded gasoline. On the other hand, the effect of ethanol–gasoline and DMC–gasoline blended fuels on NO X exhaust emission is insignificant. Using oxygen containing additives can increase fuel consumption as a result of the heating value of the blended fuels being lower than that of unleaded gasoline.

Development and Application of an Eight-Step Global Mechanism for CFD and CRN Simulations of Lean-Premixed Combustors

In this paper, the development of an eight-step global chemical kinetic mechanism for methane oxidation with nitric oxide formation in lean-premixed combustion at elevated pressures is described and applied. In particular, the mechanism has been developed for use in computational fluid dynamics and chemical reactor network simulations of combustion in lean-premixed gas turbine engines. Special attention is focused on the ability of the mechanism to predict NOx and CO exhaust emissions. Applications of the eight-step mechanism are reported in the paper, all for high-pressure, lean-premixed, methane-air (or natural gas-air) combustion. The eight steps of the mechanism are as follows: (1) oxidation of the methane fuel to CO and H2O, (2) oxidation of the CO to CO2, (3) dissociation of the CO2 to CO, (4) flame-NO formation by the Zeldovich and nitrous oxide mechanisms, (5) flame-NO formation by the prompt and NNH mechanisms, (6) postflame-NO formation by equilibrium H-atom attack on equilibrium N2O, (7) postflame-NO formation by equilibrium O-atom attack on equilibrium N2O, and (8) postflame Zeldovich NO formation by equilibrium O-atom attack on N2.

Exhaust emissions and energy release rates from a controlled spark ignition engine using ethanol blends

Although alcohols have been considered and used as fuels for internal combustion engines for decades, their use in automotive transportation systems has been rather limited. In the past few years, ethanol has received varying amounts of attention in the United States owing to the increasing cost of gasoline fuel and legislative mandates in some states requiring the sale of alcohol-blended gasoline for light-duty vehicles. This may, in the end, help the agricultural economy in the United States. If alcohol blends are to be used in spark ignition (SI) engines designed to operate on gasoline, then it is important that engines be tuned for the fuel that is being utilized at that instant. This requires knowledge of the combustion characteristics of alcohol blends so that the engine control system can make appropriate changes according to the quality of the blend. The present investigation was conducted to evaluate the combustion and exhaust emissions characteristics of ethanol-gasoline blends in a two-valve automotive SI engine. Ethanol blends improved the specific energy consumption relative to pure gasoline fuel. At stoichiometric air-fuel ratio, the alcohol blends improved exhaust CO emissions marginally. However, there were consistent reductions in NO x levels, particularly with the E-85 blend. The use of E-85 in the engine also resulted in a reduction in HC levels relative to neat gasoline, but E-85 produced significantly higher levels of acetaldehydes by comparison with neat gasoline and lower ethanol blends, particularly at lighter engine loads. The E-85 blend required a longer time to develop and set up the flame in the combustion chamber relative to neat gasoline. This was particularly true at lower engine loads, probably owing to cooling effects of the inducted charge. However, the rapid combustion duration did not exhibit much difference between the blends and gasoline.

Ethanol-Based Biodiesel from Waste Vegetable Oil

Waste vegetable oil, mainly coming from frying residues, can be used as raw material to obtain a diesel fuel (biodiesel). Biodiesel, a nontoxic, biodegradable, diesel-like fuel, is an important energy alternative capable of decreasing environmental problems caused by the consumption of fossil fuels. The utilization of waste vegetable oils as raw material in biodiesel production was studied. Research was undertaken to establish the availability of used vegetable oil to supply a biodiesel process. It is intended that this work forms an academic study combined with an environmental and technological analysis of the merits of biodiesel as a sustainable fuel. Laboratory experimentation investigated the possibility of using waste vegetable oil from the local fast food chains, and potassium hydroxide as catalyst for the transesterification process. The cleaned waste vegetable oil undergoes transesterification for 4 hours, after which, the biodiesel is separated from the glycerin by gravity. Washing is necessary to remove residual catalyst or soap. Overall material balance for the process gives: 1 kg Waste Vegetable oil + 0.18 kg EtOH + 0.01 kg KOH → 0.74 kg Biodiesel + 0.44 kg Glycerin The biodiesel, in pure form (B100) and in 50% proportion (B50) with petroleum diesel, was run in an essentially unmodified Toyota 2C diesel engine. Smoke density (opacity) and CO exhaust emission both decreased with B50. However, Nox increased with B50. Fuel consumption during engine power testing is significantly greater using the biodiesel, but is also significantly reduced with B50.

Combustion and Exhaust Emissions Characteristics in the Supercharged Engine Ignited with Gas Oil Fueled by Pyrolysis Gas Generated from Biomass

Pyrolysis gas produced from woody and waste biomass is considered as one of very important fuels to establish a sustainable society. In this study, a supercharged single cylinder gas engine with micro pilot ignition by gas oil was used. This ignition system has an advantage of large energy source, long period for ignition and stable ignition compared to the spark ignition system. Four types of artificial pyrolysis gases that were compressed into high pressure vessels were used. Compositions of these gases were H2, CO, CO2, CH4 and N2. Combustion was visualized by using a high-speed color video camera from the bottom of the quartz piston. The pressure history was analyzed to obtain the rate of heat release in order to investigate combustion characteristics. Exhaust emissions of NOx HC, CO and smoke were measured. Many ignition kernels produced by the iginition of gas oil initiate flame propagation of gas/air mixture and then flames move toward the wall of cylinder. Effects of injection timing, gas composition and equivalence ratio on engine performance were studied.

Exhaust Emissions of Biodiesel, Petrodiesel, Neat Methyl Esters, and Alkanes in a New Technology Engine

Biodiesel is a renewable, alternative diesel fuel of domestic origin derived from a variety of fats and oils by a transesterification reaction; thus, it consists of the alkyl esters, usually methyl esters, of the fatty acids of the parent oil or fat. An advantage of biodiesel is its potential to significantly reduce most regulated exhaust emissions, including particulate matter (PM), with the exception of nitrogen oxides (NOx). In this work, three fatty acid methyl esters, neat methyl laurate, neat methyl palmitate, and technical grade methyl oleate, were selected for exhaust emissions testing in a heavy-duty 2003 six-cylinder 14 L diesel engine with exhaust gas recirculation. These fuels were compared with neat dodecane and hexadecane as well as commercial samples of biodiesel and low-sulfur petrodiesel as the base fuel, thus establishing for the first time a baseline of the exhaust emissions of neat hydrocarbon (alkane) fuels versus neat methyl esters. All fuels were tested over the heavy-duty diesel transient cycle. PM emissions were significantly reduced with biodiesel and methyl oleate (about 77 and 73%, respectively), while reductions with methyl palmitate and methyl laurate were even greater (82−83%) compared to the petrodiesel fuel. PM emissions with biodiesel only slightly exceeded the upcoming emissions standards, raising the possibility that biodiesel may meet these standards using only a diesel oxidation catalyst without employing a particulate trap. NOx emissions increased with biodiesel (about 12%) and technical grade methyl oleate (about 6%) but decreased (about 4−5%) with methyl palmitate and methyl laurate relative to those of the base fuel. PM emissions decreased (about 45−50%) with both dodecane and hexadecane. NOx emissions were reduced (around 15.5−16%) with dodecane and hexadecane compared to those of the petrodiesel fuel. The methyl ester moiety influences exhaust emissions by reducing particulate matter considerably more than neat straight-chain hydrocarbons, which are enriched in “clean” petrodiesel fuels, while NOx exhaust emissions, which showed little chain-length dependence, are less reduced. Thus, no future “clean” petrodiesel fuel should be able to achieve the low PM exhaust emissions levels of biodiesel without additional additive treatments or support by engine technology. Unsaturated fatty esters show slightly increased NOx and PM emissions compared to their saturated counterparts. The soluble organic fraction of the PM emissions was higher for the ester fuels. Hydrocarbon (HC) and CO exhaust emissions were also determined. Although HC emissions were low, a strong effect of chain length was observed.

Comparison of Real-World Emissions from Two-Wheelers and Passenger Cars

Passenger cars are the primary means of transportation in Europe. Over the past decade, a great deal of attention has therefore been paid to reducing their emissions. This has resulted in notable technical progress, leading to unprecedentedly low exhaust emissions. In the meantime, emissions from motorcycles have been ignored due to their subordinate role in traffic. Even though the motorcycle fleet is small in comparison with the car fleet, and logs lower yearly mileage per vehicle, their contribution to traffic emissions has become disproportionately high. Exhaust emissions of CO, HC, NOx, and CO2 from 8 powered two-wheelers were measured and compared to previous measurements from 17 gasoline-powered passenger cars performed at EMPA with the aim of ascertaining their relevance. Using exhaust emission ratios from both vehicle types, comparisons based on mean unit, mean yearly, and fleet emissions are considered. Present-day aftertreatment technologies for motorcycles are not as efficient as those for cars. A comparison of mean unit emissions shows that motorcycles exceed cars in NOx emissions. All comparisons reveal a significant HC ratio, to the detriment of two-wheelers. Overall, the relevance of emissions from powered two-wheelers is not negligible when compared with modern gasoline-powered passenger cars.

Modelling of air pollution on a military airfield

The paper presents a numerical study of exhaust emission and pollutant dispersion of carbon monoxide on a military airfield. Investigations have been carried out for typical conditions of aircraft usage in the Polish Air Force Academy in Dęblin. Two different types of aircraft have been taken into account. One of them is an MI-2 helicopter, the second is a TS-11 plane. Both are used in military pilot education in Poland. Exhaust emission of CO from those aircrafts has been obtained in an experiment carried out on an engine test stand. CO concentrations have been calculated for different meteorological conditions (averaged from 5 years observations) and selected conditions of aircraft use. The finite volume method has been used to discretise the equation describing the process of pollutant dispersion. In addition, the two-cycle decomposition method has been employed to solve the set of ordinary differential equations of the first order obtained after discretisation of the advection–diffusion equation. A meteorological pre-processor, based on relationships resulting from the Monin–Obukhov theory, is used to define eddy diffusivity and the profile of air speed in the lower layer of the atmosphere. In the paper, the computer model and calculated average concentration of CO in the Dęblin airfield during typical flights are presented. The goal of the computational analysis is to predict CO pollution level in the workplace of aircraft service personnel.

CO, HC and NOx Emissions Characteristics of a Retrofitted Bi-fuel Natural Gas Engine

This paper presents the experimental results carried out to evaluate CO, HC and NOx exhaust emissions and performance characteristics of a computer integrated bi-fuel spark ignition engine that has been retrofitted for two fuels namely, gasoline and compressed natural gas (CNG). The ignition point was optimised for CNG through the external device so that the maximum cylinder pressure occurred at similar as gasoline fuel such as between 10 to 10.50 deg crank angles after top dead centre (TDC). The used engine is a 4-cylinder spark ignition engine that has been operated with steady state condition using engine operating software and data acquisition system called CADET6. An eddy current dynamometer was used to measure engine performance characteristics such as engine brake power and fuel consumption and to give load on engine during measuring emission characteristics. Bosch and Bacharach exhaust gas analysers were used to measure emissions gases such as CO, HC and NOx . The performance test was done with fu...

Study of the Thermal Bubble Inkjet Technology on Motorcycle Engine Application

A new fuel injection concept called micro-pulsation fuel injection (μPFi) system had been installed in a commercial 4 stroke, 125 c.c. motorcycle engine for feasibility study. The thermal bubble inkjet technology is used on the design of digital controlled μPFi system in this study. This system is composite by the arrays of the thermal bubble micro-fuel injectors, which could be operating in high ejection frequency and with fine fuel droplets into the intake pipe on engines by accurate control mode. The advantages of digital control on fuel droplet atomization are active control of fuel ejection volume and optimization of combustion efficiency. The atomized fuel droplet volumes are controlled within 100 ∼ 500 pl. The endurance test of the μPFi fuel supply assemblage had accumulated over 200 hours in a bench. It could be afforded a motorcycle to drive more than 10,000 km accumulated-mileage at constant speed 50 kph. The engine tests show that the μPFi engine improved BSFC by up to 15%, relative to carburetor engine. In addition, the motorcycle with μPFi system achieves superior exhaust CO emissions than the carburetor system while keeping comparable performance.

省エネルギー型・低公害廃油燃焼バーナーの開発研究（ＩＩ）−内部混合型二流体噴射弁による廃油の燃焼と排出ガス特性−

Waste oil, such as waste engine oil, the leftover oil from tanker ships is usually of a high viscosity, low quality and includes water. The recycling and effective use of waste materials are regarded as very important from resources saving view point. The purpose of this study was to develop a waste oil com-bustion burner, which is able to atomize high viscous waste oil using low energy and is able to reduce pollutant emissions. The waste oil combustion burner consists of an internal mixing twin-fluid atomizer and a flame holder. We investigated the effects of geometric shapes of atomizer and flame holders on the combustion characteristics of waste oil. The results indicated that high effective and stable combustion of waste oil were achieved with low energy. Moreover, the flame is mainly luminous, blow-off of the flame takes place hardly, smoke emission is little and simultaneously reduction of NOx and CO exhaust emissions was achieved independent of the fuel mass flow rate under low atomizing air mass flow rate.

Remote sensing study of emissions from motor vehicles in the Metropolitan Area of Mexico City.

Remote sensing was employed for the first time to measure nitric oxide (NO) levels of on-road light-duty motor vehicles of the Metropolitan Area of Mexico City (MAMC). The sensor placed at 12 different sites also measured the concentration of CO2, CO, and total hydrocarbons (THC) in the exhaust emissions. A database was compiled containing 122 800 readings, of which 84 650 (69%) records were valid emissions measurements. CO, HC, and NO valid readings were 68.9, 63.4, and 62.9%, respectively, of the total attempted measurements. Furthermore, 42 822 vehicles were number-plate-matched to model year with the information provided by the Inspection/Maintenance Program. The mean emissions of total valid readings for CO, HC, and NO were determined to be 1.31 vol %, 440 ppm (propane), and 914 ppm, respectively. In 1991 and 1994, remote sensing measurements of CO and HC tailpipe emissions were performed in the MAMC in five different locations (30 000 valid readings). Large drops in both pollutants were observed for the intervening years, but sufficient vehicle information was not available at that time to fully explain the observed trends. Compared with those reports, our results point out to a steady decrease in CO and HC exhaust emissions with vehicle model year. The fleet emissions measured exhibit a gamma-distribution, with 10% of the most polluting fleet studied being responsible for 45%, 25%, and 29% of the CO, HC, and NO emissions, respectively. NO emissions in taxis are the highest among the vintage of vehicles, a matter of concern since according to the distance traveled per year, they represent 22% of the total activity in the MAMC.