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Viewing 1 to 30 of 462
2013-09-24
Journal Article
2013-01-2475
Taizo Shimada, Mitsuo Notomi, Junya Tanaka, Koji Korematsu
In recent years, trans-esterified vegetable oils have been widely applied to diesel engine in order to suppress greenhouse gas emissions. However, “neat” vegetable oils are expected to be directly used to resolve some difficulties faced in their use, such high viscosity and slightly high fuel consumption. In this study neat linseed oil has been investigated as a neat vegetable oil. It was found to show higher fuel consumption than diesel fuel, however at the same time it showed lower indicated fuel consumption than diesel fuel. These results suggest some increase in engine friction loss in a neat biofuel diesel engine. Studies have been extensively investigated the difference in friction loss and a newly developed “improved deceleration method” has been applied.
2013-09-24
Technical Paper
2013-01-2451
Lian Soto Izquierdo, Gian Gomes Marques, Vanessa Balieiro
Studies aimed at partial or total use of renewable fuels in diesel engines has increasingly attracted the interest of the automotive industry, in particular due to its characteristics of strength, durability and greater thermal efficiency. The oil esters derived from biological sources, who receive the generic name for biodiesel, is one of the alternatives used internationally. Their physicochemical properties are similar to diesel oil for providing an acceptable dynamic process of preparation and combustion in the engine. This paper presents and evaluates the results of experimental tests carried out in four trucks used exclusively B20 biodiesel (20% biodiesel and 80% petroleum diesel), and one with B100 (pure biodiesel), in real operating conditions.
2013-09-24
Journal Article
2013-01-2453
Essam Oun Al-Zaini, Dean M. Chesterfield
This paper reports the optimisation study of a batch scaled ethanolysis conversion of waste frying oil carried out over aluminium phosphate-potassium bi-functional catalysts. All synthesised catalysts were analysed for their structural and surface chemical properties thereby following N2 adsorption-desorption isotherm and CO2 and NH3-temperature programmed desorption techniques respectively. X-ray diffraction and x-ray photoelectron spectroscopy were also adopted for phase identification and atomic quantification studies respectively. Ethanolysis experiments were carried out eliminating reaction rate limitations caused by solid-liquid interfacial mass transport and intraparticle diffusion. Other operating parameters were also examined in the study. These included; reaction temperature, catalyst percentage loading on support, catalyst weight and reactants molar ratio (β).
2013-09-24
Journal Article
2013-01-2422
Yu Zhang, Ilya Sagalovich, William De Ojeda, Andrew Ickes, Thomas Wallner, David D. Wickman
Low temperature combustion through in-cylinder blending of fuels with different reactivity offers the potential to improve engine efficiency while yielding low engine-out NOx and soot emissions. A Navistar MaxxForce 13 heavy-duty compression ignition engine was modified to run with two separate fuel systems, aiming to utilize fuel reactivity to demonstrate a technical path towards high engine efficiency. The dual-fuel engine has a geometric compression ratio of 14 and uses sequential, multi-port-injection of a low reactivity fuel in combination with in-cylinder direct injection of diesel. Through control of in-cylinder charge reactivity and reactivity stratification, the engine combustion process can be tailored towards high efficiency and low engine-out emissions. Engine testing was conducted at 1200 rpm over a load sweep.
2013-09-08
Technical Paper
2013-24-0110
Max Kofod, Trevor Stephenson
The EU Commission's “Clean Power for Transport” initiative aims to break the EU's dependence on imported oil whilst promoting the use of alternative fuels to reduce greenhouse gas emissions. Among the options considered is the use of liquefied natural gas (LNG) as a substitute for diesel in long haul trucks. It is interesting to ask how the lifecycle greenhouse gas (GHG) emissions of LNG compare with conventional diesel fuel for this application. The LNG available in Europe is mainly imported. This paper considers the “well-to-tank” emissions of LNG from various production routes, including: gas production, treatment and liquefaction, shipping to Europe, terminal, distribution and refuelling operations. “Tank-to-Wheel” emissions are considered for a range of currently-available engine technologies of varying efficiency relative to diesel.
2013-01-09
Technical Paper
2013-26-0015
S. S. Thipse, K. P. Kavathekar, S. D. Rairikar, A. A. Tyagi, N. V. Marathe
A duel fuel diesel engine is a diesel engine fitted with a dual fuel conversion kit to enable use of clean burning alternative fuel like compressed natural gas. Dual fuel engines have number of potential advantages like fuel flexibility, lower emissions, higher compression ratio, better efficiency and easy conversion of existing diesel engines without major hardware modifications. In view of energy depletion and environmental pollution, dual fuel technology has caught attention of researchers as a viable technology keeping in mind the increased availability of fuels like Compresed Natural Gas (CNG). It is an ecological friendly technology due to lower PM and smoke emissions and retains the efficiency of diesel combustion. Traditionally dual fuel technology has been popular for large engines like marine, locomotive and stationery engines. However its use for automotive engines has been limited in the past due to constraints of limited supply of alternative fuels.
2013-10-07
Technical Paper
2013-36-0313
Fernando Z. Sánchez, Carlos V. M. Braga, Leonardo C. Braga, Sergio L. Braga, Flávio G. Dias, Franck Y. Turkovics, Renata N. C. De Souza
Nowadays, many researches are being carried out to replace the diesel by alternative fuels. Biodiesel and ethanol are strong candidates for this purpose. However, the experimental study of the combustion of biofuels in engines is not an easy task. Due to the large differences between the properties of the new fuels and the conventional diesel, radical changes may be needed in current engines, developed specifically for the fossil fuel. So, the experimental study of ethanol compression ignition (CI) combustion is not simple to be obtained in conventional engines. Therefore, some experimental apparatus, such as a rapid compression machine (RCM), are useful to conduct this kind of study. This paper describes the RCM adaptations made in order to run CI combustion tests using Ethanol-Powered (ED95) and Diesel (S50) for different compression ratios and injection timing.
2013-10-07
Technical Paper
2013-36-0182
M. Pontoppidan, G. Montanari
The paper gives a short introduction to the bio-diesel mixture approach for diesel engines. The paper continues with a description of the design of a strategy for recognition of a random bio-diesel fraction, Bx, by a purely software-based sensing technique, which creates an image of the temporal combustion behavior and uses only sensors already in service for current common rail mixture preparation systems. A short description is made of a baseline approach of sensing technique based on the presence of a crank angle speed sensor. Hereafter the paper presents the introduction of several integral or Upper Level (UL) key-parameters used to enhance the precision of the Bx-detection or completely replace the original lower level combustion key-parameter set, which relates the instantaneous fraction of bio-diesel, Bx, to the engine torque.
2013-10-07
Technical Paper
2013-36-0209
Anibal Godoy Machado, Nilton Mitsuro Shiraiwa
With the purpose of minimizing the gaseous emissions impacts on the metropolitan areas, many alternative fuel resources has been developed as alternatives to fossil fuels. An environmentally and economical interesting alternative for the Brazilian market is the diesel made from sugar cane (Farnesene - C15H32). The Farnesene, made by sugar cane juice fermentation in presence of a genetically modified yeast is basically a saturated hydrocarbon molecule (C15H32) with more than 98% purity and that presents properties comparable to fossil diesel and when used in regular diesel cycle engines can bring significantly reductions not only in soot levels (Particulate Matter - PM) but also on the Nitrogen Oxides (NOx), unlike the biodiesel, that is well known that it brings increases on NOx emission level due its physic-chemical properties. Reduction on CO2 levels on life cycle is another important benefit of using such fuel since it's made by renewable feedstock.
2013-10-07
Technical Paper
2013-36-0208
Anibal Godoy Machado, Nilton Mitsuro Shiraiwa
With focus on reducing the Green House Gases emissions, the use of biodiesel as an alternative fuel, in special for buses that runs on the Brazilian metropolitan areas has been even higher. Additionally, with the introduction of the new legislation for diesel engines in 2012, CONAMA PROCONVE P7, that in order to attempt to its requirements uses different kinds of exhaust gases after treatment systems, the necessity of knowing the behavior of those “P7 engines” operating with different biodiesel contents on blends with regular fossil fuel or even pure biodiesel has been an important issue to ensure the benefits of using such alternative fuel. On this evaluation, blends of 5%, 10%, 20%, 30%, 50%, 75% and 100% of biodiesel content in ANP65/2011 A_S50 Diesel Fuel (50ppm Sulfur content) was experimented in a Mercedes-Benz OM926LA E5 engine with SCR (Selective Catalyst Reaction) exhaust gases after treatment system.
2013-10-07
Technical Paper
2013-36-0324
Roberto F. Britto, Eugênio P.D. Coelho, Sammi Frederico, Marcelo Machado, Daniel Martinek, Celso Rabello, Thaisa Tomita
Brazil has been a leader for the past 30 years in the development and commercialization of vehicles powered by ethanol, which contributes significantly to maintain the basic Brazilian energy less dependent on fossil fuels, but its usage was restricted to small vehicles with focus on gasoline replacement. Whereas the use of diesel fuel has significant impact on emission of greenhouse gases when it is compared to the whole production cycle of the alternative fuels (“well to wheel” analysis), these fuels have been the focus of studies, applications, federal government programs, and also the private sector, such as bio-diesel, sugar cane diesel, ethanol with additive for diesel cycle and diesel-gas Dual-Fuel. This paper will detail the development a high efficient engine fueled with 100% hydrated ethanol capable to achieve up to 42% of break efficiency, similar to a diesel efficiency running on Otto cycle.
2013-10-07
Technical Paper
2013-36-0319
Glécia Virgolino da Silva Luz, Pilar Hidalgo, Carlos Gurgel Veras, Simona Merola, Luigi Allocca, Alessandro Montanaro, Luca Marchitto
The use of biodiesel as alternative to fossil fuel for light duty CI engines to reduce greenhouse gas emissions was widely investigated. However, poor stability of biodiesel - diesel mixture limits the use of biodiesel to low volume concentrations. This paper presents the results concerning the use of a novel fuel additive package containing antioxidant (AS), pour-point depressant (D) and biocide (Bi) with the aim to increase the quality and amount of biodiesel in the diesel-biodiesel blends. Some of the goals are linked to the degradative effects due to free radicals oxidation, contamination by water and microorganisms. The interaction between two different additive packages and two biodiesel (soybean and rapeseed) - diesel blends at 20% in volume was investigated. Optical studies have been performed to characterize the spatial and temporal spray evolution both in a high pressure quiescent vessel and in an optically-accessible single-cylinder 2-stroke CI engine.
2013-10-07
Technical Paper
2013-36-0571
B. Heuser, M. Jakob, F. Kremer, Stefan Pischinger, B. Kerschgens, H. Pitsch
In order to deeply investigate and improve the complete path from biofuel production to combustion, the cluster of excellence “Tailor-Made Fuels from Biomass” was installed at RWTH Aachen University in 2007. Recently, new pathways have been discovered to synthesize octanol [1] and di-n-butylether (DNBE). These molecules are identical in the number of included hydrogen, oxygen and carbon atoms, but differ in the molecular structure: for octanol, the oxygen atom is at the end of the molecule, whereas for DNBE it is located in the middle. In this paper the utilization of octanol and DNBE in a state-of-the-art single cylinder diesel research engine will be discussed. The major interest has been on engine emissions (NOx, PM, HC, CO, noise) compared to conventional diesel fuel.
2013-10-07
Technical Paper
2013-36-0490
Nilton Mitsuro Shiraiwa, Rodrigo Mozardo, Celso Macarini da Costa, Wilson Muraro, Thomas Lemcke, Aníbal Zambotti
With the discovery of oil and gas in the pre-salt Santos and Campos basin, the supply of natural gas (NG) is expected to increase considerably, so the use of compressed natural gas (CNG) in city buses will be an important option for reducing the overall consumption of fossil diesel fuel and a reduction in operating costs in São Paulo and Rio de Janeiro Metropolitan Areas in Brazil. A vehicle with an engine that can run on pure diesel or diesel and CNG has advantage over a vehicle that works exclusively with CNG, because when there is no availability or the lack of CNG, the vehicle / engine operates with diesel only. Another benefit of this technology is the resale value in Brazil, because after the life cycle of use in theses two big cities, Urban Buses are sold country side to small cities where CNG is not available.
2013-10-07
Technical Paper
2013-36-0491
Fabio Nicora, Tiago Bahia Santos, Henrique Augusto Pires Rezende
Natural gas is considered today a real alternative to diesel for the use in commercial vehicles in Europe, China, India and United States. While in Brazil natural gas is often the energy source for industrial processes and passenger's cars, opportunities to extend its utilization in light, medium commercial vehicles and buses could become realty in Brazil and Latin America. At the date, most of 12.000 IVECO CNG vehicles are running in different European countries and different customers' applications mainly refuse collection, urban logistics and urban people transport. Trucks running with Compressed Natural Gas (CNG) represent today an opportunity to improve quality of life for communities, reducing the pollutant and noise emissions and allow, for the fleets operators, a cost saving directly related to fuel. In the 2011 IVECO Latin America started a CNG program to introduce CNG technology into Brazilian market.
2013-09-08
Technical Paper
2013-24-0106
Steven G. Fritz, John C. Hedrick, James A. Rutherford
The objective of this project was to assess the effects of various blends of biodiesel on locomotive engine exhaust emissions. Systematic, credible, and carefully designed and executed locomotive fuel effect studies produce statistically significant conclusions are very scarce, and only cover a very limited number of locomotive models. Most locomotive biodiesel work has been limited to cursory demonstration programs. Of primary concern to railroads and regulators is understanding any exhaust emission associated with biodiesel use, especially NOX emissions. In this study, emissions tests were conducted on two locomotive models, a Tier 2 EMD SD70ACe and a Tier 1+ GE Dash9-44CW with two baseline fuels, conventional EPA ASTM No. 2-D S15 (commonly referred to as ultra-low sulfur diesel - ULSD) certification diesel fuel, and commercially available California Air Resource Board (CARB) ULSD fuel.
2011-08-30
Technical Paper
2011-01-1998
Vilmar AEsoy, Per Magne Einang, Dag Stenersen, Erik Hennie, Ingebrigt Valberg
The maritime transportation sector is facing new international restrictions on exhaust emissions. NOx and SOx emissions from traditional marine fuels are a major challenge, which make natural gas a promising new clean alternative. Since the late 1980s, new concepts for medium-speed natural gas-fuelled engines have been developed, primarily for stationary power generation. This technology is currently entering the mobile sector, where Spark Ignition engines, Dual-Fuel engines and High Pressure Gas engines offer advantages such as high efficiency, low emissions and fuel flexibility. The availability of liquefied natural gas (LNG) is increasing, not least via small-scale distribution systems. In Norway, 23 coastal traffic vessels operate on LNG supplied by a distribution system that also supplies city bus fleets. This paper discusses the development of natural gas engines and fuel system technology, and describes experiences from LNG-fuelled ships in operation in Norway.
2011-08-30
Journal Article
2011-01-1961
Takashi Hara, Naoki Shimazaki, Naoki Yanagisawa, Takeshi Seto, Shigehisa Takase, Takeshi Tokumaru, Takurou Mita, Takeshi Okamoto, Yoshio Sato
Study of DME diesel engines was conducted to improve fuel consumption and emissions of its. Additionally, DME trucks were built for the promotion and the road tests of these trucks were executed on EFV21 project. In this paper, results of diesel engine tests and DME truck driving tests are presented. As for DME diesel engines, the performance of a DME turbocharged diesel engine with LPL-EGR was evaluated and the influence of the compression ratio was also explored. As for DME trucks, a 100,000km road test was conducted on a DME light duty truck. After the road test, the engine was disassembled for investigation. Furthermore, two DME medium duty trucks have been developed and are now the undergoing practical road testing in each area of two transportation companies in Japan.
2011-08-30
Technical Paper
2011-01-1962
Fredrik Konigsson, Per Stalhammar, Hans-Erik Ångström
Diesel Dual Fuel, DDF, is a concept where a combination of methane and diesel is used in a compression ignited engine, maintaining the high compression ratio of a diesel engine with the resulting benefits in thermal efficiency. One benefit of having two fuels on board the vehicle is the additional degree of freedom provided by the ratio between the fuels. This additional degree of freedom enables control of combustion phasing for combustion modes such as Homogenous Charge Compression Ignition, HCCI, and Partly Premixed Compression Ignition, PPCI. These unconventional combustion modes have great potential to limit emissions at light load while maintaining the low pumping losses of the base diesel engine. A series of tests has been carried out on a single cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners.
2011-08-30
Technical Paper
2011-01-1959
Xiaomin Xie, Zhen Huang
This study provides an LCA of coal derived DME vehicle fuel cycle. Two DME production systems were evaluated, one is single DME production system, and the other is DME/IGCC cogeneration (polygeneration) system. The effects of CCS technology on energy use and GHG emissions were analyzed. For single DME production design, WTW total energy use and fossil energy is about 80% larger than that for petroleum diesel production, and increases life-cycle GHG emissions by more 200% relative to petroleum diesel. Results for DME/IGCC production design pathway from displacement method are almost the same with the petroleum diesel pathway. CCS incurs an energy penalty of 7-16%.
2011-08-30
Technical Paper
2011-01-1965
Reijo Makinen, Nils-Olof Nylund, Kimmo Erkkilä lng, Pirjo Saikkonen, Arno Amberla
Helsinki Region Transport, Neste Oil, Proventia Emission Control and VTT Technical Research Centre of Finland carried out a 3.5 year PPP venture “OPTIBIO” to demonstrate the use of paraffinic renewable diesel (hydrotreated vegetable oil HVO) in city buses. The fleet test in Metropolitan Helsinki involving some 300 buses is the largest one in the world to demonstrate this new fuel. The fuels were a 30 % blend of renewable diesel and 100 % renewable diesel. This paper describes the overall set-up of the project, gives an overview of the emission results as well as presents experience from the field.
2011-08-30
Technical Paper
2011-01-1966
Kimmo Erkkilä, Nils-Olof Nylund, Tuomo Hulkkonen, Aki Tilli, Seppo Mikkonen, Pirjo Saikkonen, Reijo Makinen, Arno Amberla
When switching from regular diesel fuel (sulfur free) to paraffinic hydrotreated vegetable oil (HVO), the changes in fuel chemistry and physical properties will affect emission characteristics in a very positive way. The effects also depend on the technology, after-treatment and sophistication of the engine. To determine the real effects in the case of city buses, 17 typical buses, representing emission classes from Euro II to EEV, were measured with HVO, regular diesel and several blended fuels. The average reduction was 10% for nitrogen oxides (NOx) and 30% for particulate matter (PM). Also some engine tests were performed to demonstrate the potential for additional performance benefits when fuel injection timing was optimized for HVO.
2011-08-30
Technical Paper
2011-01-1964
Toru Miyamoto, Hirokazu Hasegawa, Takashi Yagenji, Takehiko Seo, Masato Mikami, Hajime Kabashima, Tomoyuki Hashimoto
The present study experimentally investigated cyclic variation of combustion characteristics of a diesel engine with hydrogen added to the intake air in detail. As the result, there were three ignition modes: (1) hydrogen ignition mode, (2) hydrogen-assisted ignition mode, and (3) diesel-fuel ignition mode. Ignition timing fluctuated from cycle to cycle in each ignition mode and between one ignition mode and another mode. As the coolant temperature was increased, the number of cycles in diesel-fuel ignition mode decreased, and indicated thermal efficiency and cyclic variation was improved. In the case with the blow-by gas introduced to intake port, preflame reaction of blow-by gas first occurred, ignited hydrogen, and then diesel-fuel was ignited by hydrogen combustion in hydrogen ignition mode and hydrogen-assisted ignition mode.
2011-08-30
Technical Paper
2011-01-2022
Mehrzad Kaiadi, Per Tunestal, Bengt Johansson
Abstract Stoichiometric operation of Spark Ignited (SI) Heavy Duty Natural Gas (HDNG) engines with a three way catalyst results in very low emissions however they suffer from bad gas-exchange efficiency due to use of throttle which results in high throttling losses. Variable Geometry Turbine (VGT) is a good practice to reduce throttling losses in a certain operating region of the engine. VTG technology is extensively used in diesel engines; it is very much ignored in gasoline engines however it is possible and advantageous to be used on HDNG engine due to their relatively low exhaust gas temperature. Exhaust gas temperatures in HDNG engines are low enough (lower than 760 degree Celsius) and tolerable for VGT material. Traditionally HDNG are equipped with a turbocharger with waste-gate but it is easy and simple to replace the by-pass turbocharger with a well-matched VGT.
2011-09-13
Technical Paper
2011-01-2230
Zhiyong Zhang
In this study, a measurement system is developed for obtaining continuous piston temperatures in a working engine by using a voltage recorder. The developed system has a very high accuracy with a measurement error within ± 1 °C. Since there is no relative movement between the measurement system and the piston, its reliability significantly increases. In order to test its accuracy and reliability, the developed measurement system is used to obtain the piston temperatures under various operating conditions with different air-fuel ratios, oil temperatures, and engine speeds. The measurement results are then used to calibrate the piston temperature field simulated by numerical analysis.
2011-09-13
Technical Paper
2011-01-2224
Sundarapandian S
Diesel engines dominate the field of commercial transportation and agricultural machinery on account of its superior fuel efficiency. Cost and limited reserves of conventional fossil fuels have intensified the search for alternative fuels for use in internal combustion engines. A possible alternative engine fuel is vegetable oil because it is clean burning, renewable, non-toxic, biodegradable and environmentally friendly transportation fuel. It can be used in neat form without any modification of the engine. They can be produced from the plants grown in rural areas. Vegetable oils are produced from crops such as soybean, peanut, sunflower, cotton, jatropha, mahua, neem, coconut, linseed, mustard, karanja, rape and castor. However they cause serious problems such as carbon deposits buildup, poor durability, high density, high viscosity, lower calorific value, more molecular weight and poor combustion. These problems can be rectified by transesterification process.
2011-09-13
Journal Article
2011-01-2226
Essam Oun Al-Zaini, John Olsen, Tuan Huy Nguyen, Adesoji Adesina
Developing relatively cheap and widely available resources for heterogeneous solid catalyst synthesis is a promising approach for biodiesel fuel industry. Seashell which is essentially calcium carbonate can be used as a basic support for transesterification heterogeneous catalysts. In the present investigation, the alcoholysis of waste frying oil has been carried out using seashell-supported K₃PO₄ as solid catalyst. The rationale for this derives from the fact that waste frying oil contains both long-chain free fatty acids (FFA) and triglycerides (TG) which are catalyzed on acid and basic sites respectively. Thus, the K₃PO₄/seashell catalyst may serve the dual role of promoting both esterification and transesterification reactions. The catalyst was synthesized following a dipping impregnation of pre-crushed and calcined seashell in an aqueous solution of K₃PO₄. Samples with different percentage loadings of K₃PO₄ (5 to 25 wt%) were prepared.
2011-09-13
Technical Paper
2011-01-2223
Fredrik Königsson, Per Stalhammar, Hans-Erik Angstrom
Diesel Dual Fuel, DDF, is a concept which promises the possibility to utilize CNG/biogas in a compression ignition engine maintaining a high compression ratio, made possible by the high knock resistance of methane, and the resulting benefits in thermal efficiency associated with diesel combustion. A series of tests has been carried out on a single-cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners. One feature of port-injected Dual Fuel is that full diesel functionality is maintained, which is of great importance when bringing the dual fuel technology to market. The objective of the study was to characterize and investigate the potential for dual fuel combustion utilizing all degrees of freedom available in a modern diesel engine. Increased diesel pilot proved efficient at reducing NOx emissions at low λ.
1999-08-17
Technical Paper
1999-01-2906
W. D. Jacobs, L. K. Heung, T. Motyka, W. A. Summers, J. M. Morrison
The H2Fuel Bus is the world's first hydrogen-fueled electric hybrid transit bus (see Figure1.). It was a project developed through a public/private partnership involving several leading technological and industrial organizations, with primary funding by the Department of Energy (DOE). The primary goals of the project were to gain valuable information on the technical readiness and economic viability of hydrogen fueled buses and to enhance the public awareness and acceptance of emerging hydrogen technologies. The bus completed its field-testing and was placed into public service on September 4, 1998 by Augusta Public Transit in Augusta, Georgia. The bus employs a hybrid Internal Combustion (IC) engine/generator and battery powered electric drive system, with onboard storage of hydrogen in metal hydride beds.
1999-11-15
Technical Paper
1999-01-3738
Bruce E. Finley, Tracy A. Daly
This report details the experiences of two California public transit agencies that replaced aging diesel buses with new compressed natural gas (CNG) buses in 1994. The operating characteristics and costs of 170 natural gas buses are compared with 73 older diesel buses. The natural gas bus fleets have operated well and led to cost reductions in both fleets. The findings are particularly significant because both Sacramento Regional Transit District (RT) and SunLine Transit Agency have been using the same engine-chassis configuration, thus enabling a valid method to combine cost data for a large sample fleet of buses. The data indicate that labor for diesel equipment was almost twice that for CNG vehicles, parts were 25% more and fuel costs were nearly double. In 1997, CNG buses saved RT over $1 million in fuel, maintenance, parts and hazardous waste disposal, a 38% per mile reduction over the cost of their older diesel buses.
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