Bioethanol Blends Research Articles

KARAKTERISTIK DAN POTENSI BIOETANOL DARI NIRA NIPAH (Nypa fruticans) UNTUK PENERAPAN SKALA TEKNOLOGI TEPAT GUNA

Implemetasi underdeveloped research for large-scale production of energy selfsufficient villages and confined in a laboratory scale. The presence of mangrove forests along the palm beach peissir Indonesia is a potential independent village granaries Energy (DME) to produce local non-fossil energy resources, namely bioethanol as an energy mix through the substitution of fossil fuels in order to add and save energy nationwide. Exploration of green energy production process Tempatan with scale appropriate technology is essential to know the characteristics and potential of bioethanol and fuel substitution products will be produced. The purpose of this study was to determine the characteristics of bioethanol from palm sap processing to scale the application of appropriate technology and the potential value of bioethanol FGE levels that would result in a 1 ha of mangrove forests nypa. Research using experimental and observational methodologies. Palm sap is used as the subject of this study is the result of tapping mangrove palm bunches done processing fermentation, distillation and dehydration. Data collected includes data 1). Characteristic, among others: fermentation, Kadar Alcohol Distillation and Dehydration results TTG Tools, Redemen Bioethanol, Nipah Bioethanol Quality Testing Specifications for Substitute Grade Fuel, Bioethanol Blending Testing FGE The substitution process to Fossil Fuels and Counting Bioethanol substitution needs to Biopremium octane FGE 92-95. And data 2). The potential value of Bioethanol and Biopremium Nipah. Furthermore, the data obtained and analyzed, if there is a significant difference followed by Duncan test at 5% significance level. The results showed the characteristics of bioethanol from palm sap processing to scale the ISSN 1978-5283

Fuzzy Inoperability Input-output Analysis of Mandatory Biodiesel Blending Programs: The Philippine Case

Biofuels are regarded as one of the major low-carbon energy options currently available for large-scale use. Many countries have implemented biofuel programs that involve blending of bioethanol with gasoline, or biodiesel with diesel, at varying proportions. These programs are designed to address pressing concerns such as climate change, environmental quality, energy security and rural development. However, recent works suggest that biofuel resources may be at risk due to aberrant climatic events that are anticipated in the near future. Potential climate-induced disruptions include changes in precipitation levels, pest infestation, plant diseases, or increased frequency of extreme weather events. The incidence of such disruptions not only affects biofuel producers, but also energy-dependent economic sectors, resulting to “ripple effects” that further increase economic losses. We apply the inoperability input-output model (IIM) proposed by Haimes and Jiang (2001) and later enhanced by Santos and Haimes (2004) to assess the economic effects of implementing mandatory biodiesel blending programs in the Philippines. The IIM is based on the well-established technique of input-output analysis that quantifies risk through the inoperability metric, which is a dimensionless index whose value ranges from 0 (for a system functioning normally) to 1 (for a system in a state of total failure). Using the IIM, we determine the adverse effects of climate-induced biofuel disruptions on interdependent economic sectors. We estimate the resulting crop losses using the storm damage scenario from Stromberg et al. (2011) under no blending and a proposed blending rate of 5% as considered by the Department of Energy. Different ranking strategies are evaluated to determine sector vulnerability using inoperability levels, economic losses and weighted inoperability levels. For the latter scenario, equal weights are considered. Uncertainties within the modelling framework are captured through the use of fuzzy numbers.

Effects of blends on the physical properties of bioethanol produced from selected Nigerian crops

Bioethanol fuel was synthesised from various Nigerian crops (palm (Elaeis Guineensis) wine, raffia (Raphia vinifera) trunk and sugar cane (Saccharum L.)) to serve as alternative fuels for internal combustion engines. Bioethanol was obtained through fermentation and distillation from these selected Nigerian crops and was then purified. Physical properties of the bioethanol and various petrol–bioethanol blends such as vapour pressure, octane number, flash point, heating values, auto ignition temperature and density were evaluated using the American Society for Testing and Materials methods. The calorific value of petrol decreased from 44.40 to 44.22 MJ/kg with a blend of 10% of alcohol (E10). The calorific value of the produced ethanol (E100) is 29.78 MJ/kg. The research octane number (RON) of petrol increased from 91 to 94 with a blend of 10% of alcohol (E10). The RON of the produced ethanol (E100) is 114. The flash point increased from -40°C at E10 to 12.6°C at E100. The results showed that the addition of bioethanol to petrol increases the octane number, flash point and auto ignition temperature, but on the other hand reduces the calorific value of the produced blend. The optimal petrol–bioethanol blends of E20 and below were recommended for vehicles running on spark ignition engines.

Cellulosic ethanol production from agricultural residues in Nigeria

Nigeria′s Biofuels Policy introduced in 2007 mandates a 10% blend (E10) of bioethanol with gasoline. This study investigates the potential for the development of a cellulosic ethanol industry based on the availability of agricultural residues and models the number of commercial processing facilities that could be sited in the six Geo-political zones. The potential for cellulosic ethanol production from agricultural residues in Nigeria is 7556km3 per annum exceeding the mandate of 10% renewable fuel required and providing the potential for 12 large- and 11 medium-scale processing facilities based on the use of a single feedstock. Cassava and yam peelings provided in excess of 80% of the process residues available with enough feedstock to supply 10 large-scale facilities with a fairly even distribution across the zones. Sorghum straw, millet straw and maize stalks represented 75% of the potential resource available from field residues with the potential to supply 2 large- and 7 medium-scale processing facilities, all of which would be located in the north of the country. When a multi-feedstock approach is used, this provides the potential for either 29 large- or 58 medium-scale facilities based on outputs of 250 and 125km3 per annum respectively.

Injection parameter optimization by DoE of a light-duty diesel engine fed by Bio-ethanol/RME/diesel blend

An experimental campaign has been devoted to characterize the engine fuelled by the ethanol based blend highlighting the advantages and issues related to the bio-ethanol use. The effects of the most important injection settings on the engine performance have been detailed, applying a Design of Experiment (DoE) method, to identify the most important parameters affecting emissions and the potentiality offered by a proper engine calibration to optimize the ethanol blend use. The tests were performed on a 2.0L Euro 5 diesel engine, in steady-state at partial and full-load conditions, burning two fuel blends: a Rapeseed Methyl Ester (RME)/diesel blend with 10% of biodiesel by volume, assumed as reference fuel, and a bio-ethanol/RME/Diesel with 20% of bio-ethanol and 10% of biodiesel by volume. Emission measurements with standard Euro 5 calibration showed the well-know effects of ethanol blending to diesel fuel: a strong smoke emissions reduction in all tested conditions, together with a decrease of NOx exhaust concentration. An increment of CO and HCs emissions for bio-ethanol blends were also found, mainly at low load conditions. This issue has been investigated performing a specific test campaign inspired to the DoE method. Such activity identified in the calibration of the pilot injection quantity and rail pressure values the most influential factors in the gaseous unburned reduction. By the adoption of an optimized calibration, identified by DoE results, gaseous emissions on NEDC cycle were significantly reduced with respect to the reference calibration, matching the HCs and CO Euro 5 limits and approaching both PM and NOx Euro 6 emission levels.

Production of renewable and sustainable fuel from Calliandra calothyrsus and its utilisation in compression ignition engines

Alternative fuels have several advantages compared to fossil fuels as they are renewable, biodegradable, provide energy security, foreign exchange saving as well as help in addressing environmental concerns and socio-economic issues. Therefore, renewable fuels can be used predominantly as a fuel for transportation and for applications in power generation. Shaft power application is a key factor for economic growth and prosperity and depends crucially on the long-term availability of energy from sources that are affordable, accessible and environmentally friendly. In this context, the main objective of the present study was to implement the production of bioethanol from Calliandra calothyrsus, a potential lignocellulosic raw material for the cellulose-to-bioethanol conversion process that can be used as an alternative resource to starch- or sugar-containing feedstock. This study addresses a new pretreatment method known as hydrothermal explosion using C. calothyrsus for ethanol production. The present study also involves experimental investigations on a single-cylinder, four-stroke, direct-injection diesel engine operated with Honge oil methyl ester (biodiesel) and ethanol and its comparison with a neat diesel fuel mode of operation. The results revealed that optimal parameters for bioethanol production from C. calothyrsus were 2% acid concentration (HCl), 100°C temperature and 80 min retention time. For a diesel engine operated with a HOME–bioethanol blend, the experimental results showed a 3–4% decrease in brake thermal efficiency with a 8–10% increase in hydrocarbon and carbon monoxide emission levels and a 15–18% decrease in nitric oxide emission levels when compared with a neat diesel fuel mode of operation.

Predicting the temperature dependent density of biodiesel–diesel–bioethanol blends

Density is a very important fuel property because it influences production, transportation, and distribution processes as well as all processes that take place in the internal combustion engine. Elaborating models to describe the density of biodiesel–diesel–bioethanol blends with a high content of biofuel facilitates the production of blends that comply with the standard quality requirements for density and the modeling and simulation of injection and combustion processes. For predicting density of rapeseed oil biodiesel–diesel–bioethanol and used cooking oil biodiesel–diesel–bioethanol blends, 2×15 ternary mixtures were prepared, having a maximum amount of biofuel of 30%v/v. The concentration of biodiesel and bioethanol varies between 5% and 25%, in increments of 5%. Their density values were determined in 15 steps in the temperature range of 273.15–343.15K. Based on experimental density values of components and blends, common linear mixing rules were evaluated, obtaining an average relative deviation under 0.125% and a regression coefficient above 0.996. In order to improve accuracy, four new mixing rules with different complexities were elaborated. The temperature dependent density of components was modeled based on experimental density values and constituents composition by linear and polynomial regression, by free version of Rackett equation and by group contribution methods. The elaborated mixing rules were tested for various combinations of component densities, yielding a very good accuracy, with an average deviation of under 0.053%. Taking into account the complexity and accuracy of the elaborated models, recommendations were made regarding their uses according to their concrete applications.

HC and CO emissions reduction by early injection strategy in a bioethanol blended diesel-fueled engine with a narrow angle injection system

The main purpose of this study was to investigate how a narrow angle injector affects the combustion and exhaust emissions characteristics in a single-cylinder diesel engine fueled by diesel–bioethanol blends. This study focused on reducing HC and CO emissions in the exhaust emissions by the bioethanol blending of diesel. A narrow angle injector with an injection angle of 70° was used and compared with a conventional angle injector having a 156° injection angle. The bioethanol was blended with the conventional diesel up to 30% with 5% biodiesel. Experiments revealed that, in a narrow angle injector, the premixed combustion duration increased with bioethanol contents unlike the similar value of conventional injector. The premixed combustion phasing decreased with the increase of bioethanol in both injectors. The variation in the peak combustion pressure of the narrow angle injector was smaller than that of a conventional injector. In addition, the narrow angle injector induced a higher indicated mean effective pressure (IMEP) and a shorter ignition delay compared to the conventional injector. In terms of exhaust emissions characteristics, the low and stable ISHC and ISCO emissions can be achieved through the application of narrow angle injector to the diesel–bioethanol blends combustion. By the early injection combustion strategy, ISHC and ISCO emissions are significantly reduced.

Partial equilibrium analysis of the EC bioethanol blend mandate policy: its potential implications for EU transport sector

The aim of this study is to set up an EU27 bioethanol partial equilibrium model under a binding blend mandate and to determine the bioethanol market clearing conditions’ implications on EU transport sector. Bioethanol supply is derived from EU27 bioethanol crops while its demand is a derived from that of transport fuel in the region. Results show that equilibrium bioethanol quantities at 70% tax rebate for the bioethanol component of the fuel mixture are 133 and 188 thousand barrels of bioethanol per day at 5.75% and 10% blend mandate respectively. This implies that a 5.75% and 10% blend mandate will decrease gasoline demand by 42% and 52% respectively from reference 2004 EU gasoline demand. Theoretically therefore, the EC biofuel blend mandate could reduce carbon foot print in the region but with questionable sustainable allocation of resources given the impact such a mandate will have on bioethanol crops commodities markets.

Effect of Bioethanol Blended Diesel Fuel and Engine Load on Spray, Combustion, and Emissions Characteristics in a Compression Ignition Engine

Effect of Bioethanol Blended Diesel Fuel and Engine Load on Spray, Combustion, and Emissions Characteristics in a Compression Ignition Engine

Impact of biodiesel in bioethanol blended diesel on the engine performance and emissions characteristics in compression ignition engine

In engine combustion studies of bioethanol blended diesel fuels, biodiesel is a very important blending fuel for preventing phase separation between diesel and bioethanol. The purpose of this study is to investigate the impact of biodiesel in bioethanol blended diesel fuel on ignition delay, premixed combustion phasing, engine performance and exhaust emissions characteristics. In this work, the fuel properties of diesel–bioethanol blends were measured and engine tests were conducted using a single cylinder diesel engine.Based on the experimental results, we found that increasing the biodiesel blending ratio recovered the reduced fuel density and cetane number of bioethanol blended diesel fuel, while the kinematic viscosity and surface tension both increased. In addition, the lower heating value (LHV) slightly decreased when biodiesel fuel was added. By increasing the blending ratio of biodiesel fuel, the ignition delay and the premixed combustion phasing advanced, and the IMEP decreased. However, the premixed combustion duration in all tested blended fuels showed almost similar values, regardless of the biodiesel contents. Biodiesel blending decreased the EI-HC emission in wide engine operating regions. In addition, for the premixed combustion phasing and ignition delay, the increase of biodiesel fuel influenced the decrease of EI-HC emission. In the case of EI-CO and EI-soot emissions at advanced injection timings (around 30° BTDC), when the combustion occurred in the squish area of the combustion chamber, the biodiesel blending impact was clear. The increase of biodiesel fuel reduced EI-CO and EI-soot emissions. In addition, the increase of biodiesel fuel slightly reduced the EI-NOx emission.

Effect of early injection strategy on spray atomization and emission reduction characteristics in bioethanol blended diesel fueled engine

This study is to investigate the emission reduction characteristics of bioethanol blended diesel fuel at early injection condition including spray, atomization and evaporation characteristics. The spray atomization and evaporation characteristics were investigated using spray visualization system and KIVA-3V code, respectively. In this work, the effect of ethanol blending on the spray behavior is more evident at early injection condition. In the calculation results, the droplet size of bioethanol blended fuel was smaller than that of diesel, and bioethanol blended diesel droplets firstly evaporated by its volatility and superior atomization characteristics. In early injection condition, the bioethanol blending caused an increase in indicated mean effective pressure with an extension of the ignition delay. The cooling effect of the bioethanol fuel reduced NOx. The HC emission increased and the CO emission decreased because of the ethanol blending. The geometry mean diameter and total number density increased as a result of ethanol blending, the particle number in the nuclei mode decreased, and the particle number in the accumulation mode increased in early injection condition.

Predicting the Temperature Dependent Viscosity of Biodiesel–Diesel–Bioethanol Blends

Viscosity is an important property of fuels for internal combustion engines and has normative values in quality standards for commercial fuels used in compression ignition engines. Elaborating reliable models to estimate viscosity of biodiesel–diesel–bioethanol blends is useful to blend fuels with high biofuel content that comply with the values of viscosity imposed in quality standards and to model and simulate injection and combustion processes for such fuels. For predicting viscosity of rapeseed oil biodiesel–diesel–bioethanol blends, 15 ternary mixtures were prepared, having a maximum amount of biofuel of 30% v/v. The concentration of biodiesel and bioethanol varies between 5% and 25%, in increments of 5%. Their density and viscosity were determined in nine steps in the temperature range 273.15–343.15 K. Using experimental data, a number of models to estimate the viscosity of liquid substances were evaluated, including Kay’s rule, simple and weighted semi-logarithmic model, and Refutas model. A simple additive model was proposed, named Kay’s weighted rule. The models used to describe viscosity of biodiesel–diesel–ethanol blends were critically evaluated and compared on the basis of the correlation coefficient and the percent relative deviation, demonstrating that the model proposed here provides the most accurate estimates for viscosity of biodiesel–diesel–bioethanol blends.

Ethanol fermentation for main sugar components of brown-algae using various yeasts

The conversion of marine biomass to renewable energy was widely considered an alternative to fossil fuel, especially with regards to bio-ethanol blending in gasoline. Due to the absence of carbohydrate content, brown algae was expected to be possible organism for achieving ethanol production, but the selected microorganism needs to effectively ferment. We carried out experiments with 8 types of yeast affiliated with each different family for ethanol production and tested the effects of different carbon sources. Low concentrations of substrate were found to mostly increase the cell growth from all different substrates, but a significant increase in ethanol production was detected on the mannitol substrate. Saccharomyces cerevisiae (KCCM50550) was found to produce the highest result among all yeast strains, and ethanol production reached 2.59 g/L from 10.0 g/L of mannitol. A higher content of ethanol production in the fermentation was evident when the carbon source concentration increased.

A study of the effects of diesel–biodiesel–bioethanol fuels on emission reduction in a compression ignition engine

This study describes the effects of diesel–biodiesel–bioethanol blending fuels on the combustion and emission characteristics of a compression ignition engine. The experiments were investigated for various blending ratios and various fuel injection parameters. In this study, biodiesel fuel was blended not only to prevent phase separation between bioethanol and diesel but also to compensate for the low viscosity of bioethanol. The bioethanol blending ratio is restricted up to 30 vol. % to maintain the ignition characteristics. The results showed that the ignition delay was extended and that the fuel consumption and the maximum rate of pressure rise deteriorated with increasing bioethanol blending ratio. In addition, the diesel–biodiesel–bioethanol fuel reduced the indicated specific soot emissions. As the bioethanol blending ratio is increased, the indicated specific carbon monoxide (CO), the indicated specific unburned hydrocarbon, and the indicated specific nitrogen oxide emissions increased slightly.

Standardization: an important tool in transforming biofuels into a commodity

Presently the world is preoccupied with concerns of soaring oil prices, energy insecurity, and increasing challenges to minimize emissions of green house gases. All these issues certainly call for major reexamination of fossil energy based present technological paradigms and in favor of decisions on investments in clean energy, which supports sustainable development. Many official documents show that the world has already acknowledged this shifting scenario, as investments in renewable energy have been growing on a steady trajectory. According to data presented by the United Nations, green energy overtook fossil fuels in attracting investment for power generation for the first time in 2008. The trend has been confirmed by the last report of UNEP, Global Trends in Renewable Energy Investment 2011, which states that in 2010 there has been a 32% rise in green energy investments worldwide. In this context, the production of biofuels on a large scale has become a dominant focus for technical and political discussions all over the world, aimed at diversifying the energy mix of countries. Nations that are capable of innovating through sound investments and breakthrough achievements will enjoy tremendous advantages, both because these emerging technologies will support their industrial expansion as well as the likelihood that high value-added exports can be generated. The enthusiasm surrounding the biofuels sector has led many countries to introduce policies of offering subsidies to stimulate the production of bioethanol and biodiesel. To speed up their introduction in the energy portfolio, a growing number of governments have been requiring that biofuels be blended with fossil fuels. In USA, for instance, bioethanol blended with gasoline can contain as high as 85% bioethanol from corn (E85), or more usually other mixtures, such as E10 and E20. Similar to bioethanol, biodiesel mixtures are denominated ‘‘BXX,’’ X being the percentage of biodiesel, e.g., B2 means 2% of biodiesel, B5, 5%, up to B100. Brazil is the most traditional economy in the production of bioethanol from sugarcane, where the first governmental decree establishing a 5% blend of bioethanol with gasoline was issued in 1931. Since then, the composition has varied and nowadays is set up to around 20%, depending on the price of the fuels. Besides, in Brazil, it is possible to find vehicles that run solely on bioethanol. Moreover, the so-called flex-vehicles can run on any mixture of gasoline and bioethanol. The country has also been making sound investments for the production of biodiesel, aiming to reach a composition level of B8 in 2013. More recently, the strategy of many producing countries, including Brazil, has moved to the forefront of turning biofuels into a full-fledged world commodity. Measures taken by some countries to protect domestic markets have been continually distorting international market of commodities for decades. Most evident and traditional measures have been related to tariffs and quotas, but other more subtle measures have been taken as well, such as subsidies to domestic producers and too harsh technical requirements. H. S. Brandi (&) R. J. Daroda T. L. Souza National Institute of Metrology, Quality and Technology (Inmetro), Av. Nossa Senhora das Gracas 50, Xerem, Duque de Caxias, RJ 25250-020, Brazil e-mail: hsbrandi@inmetro.gov.br

Energy Security, Food Security, and Economics of Sugarcane Bioethanol in India

Energy security has been an important global policy issue for more than 4 decades. Transport biofuels like bioethanol have been receiving increased attention in recent years as a solution to heavy dependence on imported petroleum fuels, which brings destabilizing price effects on the economy and causes serious environmental problems like climate change. India’s biofuel policy proposes an ambitious target of replacing 20% of petrol by blending bioethanol by 2017. This paper examines the economic feasibility of sugarcane bioethanol in India while considering food security as a competing policy priority. The analyses show that 20% blending of bioethanol cannot be achieved without affecting food production in India at the current level of productivity. Moreover, the cost of sugarcane bioethanol production exceeds the social benefits, hence use of sugarcane bioethanol cannot be justified on economic grounds. Molasses, a byproducts of sugar manufacturing, can support up to 5% blending on bioethanol without compromising food production while improving social welfare. Given that first-generation bioethanol has limited scope in the country, India’s ambitions to enhance energy security should rely on second-generation bioethanol technologies, which require improvements to become commercially viable.

Spray and Engine Performance Characteristics of Biodiesel and Its Blends with Diesel and Ethanol Fuels

The authors aimed to investigate the fuel-atomization, combustion, and exhaust emissions characteristics of dual component fuels. The analysis revealed that the blending of diesel or bioethanol fuel slightly affected the reduction of the spray tip penetration and had little influence on the variation of the spray cone angle. The droplet size of biodiesel fuel was reduced by blending with diesel or bioethanol fuel with low kinematic viscosity and surface tension. Regarding the combustion characteristics, B80D20 fuel had the same combustion characteristics as B100. However, the blending of bioethanol fuel with biodiesel fuel caused an extension of the ignition delay and a decrease of the peak combustion pressure. There was little difference in the exhaust emissions characteristics caused by the blending of diesel fuel. However, EI-NOx emissions were reduced significantly by the blending of bioethanol fuel. However, EI-HC and EI-CO emissions were increased by blending the bioethanol fuel.

米国におけるバイオエタノール混合率引き上げが国際とうもろこし需給に与える影響

The production and utilization of biofuel is promoted in the U.S., and it is estimated that the U.S. biofuel market will continue to expand in the future. The Environmental Protection Agency (EPA) decided partially waiver to allow gasoline that contains up to 15 volume percent bioethanol (E15) for certain motor vehicles on October 13, 2010. EPA approved the waiver for 2007 and newer passenger cars, light trucks including sports utility vehicles (SUV). This study uses dynamic partial equilibrium model to examine how the increasing U.S. bioethanol blend ratio on the world corn market. The baseline projection is based on a series of assumptions about the general economy, agricultural policies, and technological growth in all countries and regions during the projection period. In addition to this, it is assumed that gasoline stations in Mid-West states would install E15 equipments for certain vehicles. This study supposes two scenarios to compare with baseline scenario. If the U.S. government doesn't grant the waiver, world corn price would decrease by 1.10% in 2011/12 and 4.14% in 2020/21. In addition to this, if gasoline stations in all U.S. states install E15 equipments, world corn price will increase by 5.03% in 2011/12 and 14.01% in 2020/21. The results of this study indicate that the increasing of U.S. bioethanol blend ratio will impact on the world corn market and their impact will increase gradually from year to year.

Zig‐zagging into the future: the role of biofuels in India

AbstractIndia announced a long‐awaited and much‐needed national biofuel policy in December 2009 with a mandate of achieving 20% blending of bioethanol and biodiesel by 2017. However, while the determination of specific time‐bound targets is a crucial step in the Indian biofuel program, several aspects of the guidelines reflect uncertainty that may render the 20% target unachievable. This perspective traces the rapid changes in political strategies of biofuels in India over the last decade and reviews significant scientific progress, achieved in the same period. Our observation indicates that biofuel policies in India have followed a zigzag course interspersed with several positive initiatives, severely discouraging advocacies and occasional neglect of biofuels. The multiplicity of related policies, each partially addressing biofuel issues have amounted to increasing ambiguity.We present an analysis of the tenets of the current policy with respect to land availability, related land use, and economic and marketing institutions, which are some of the important determinants of success for the Indian biofuel program. Some recommendations emanating from the analysis are (1) to estimate of available land and land use change effects; (2) to build resilience for energy crops towards climate change; and (3) to strengthen marketing and financial mechanisms at grass‐roots level. In conclusion we emphasize the need for timely scientific assessments and the subsequent incorporation into policy formulation to enable India to achieve the overall goal of sustainable biofuel production. © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd