Production of biodiesel from waste fryer grease using mixed methanol/ethanol system

Transesterification of waste fryer grease (WFG) containing 5–6 wt.% free fatty acid (FFA) was carried out with methanol, ethanol, and mixtures of methanol/ethanol maintaining the oil to alcohol molar ratio of 1:6, and initially with KOH as a catalyst. Mixtures of methanol and ethanol were used for transesterification in order to use the better solvent property of ethanol and rapid equilibrium using methanol. Formation of soap by reaction of FFA present in WFG with KOH instigated difficulty in the separation of glycerol from biodiesel ester. To untangle this problem, two-stage (acid and alkali catalyzed) method was used for biodiesel synthesis. More than 90% ester was obtained when two-stage method was used compared to ∼ 50% ester in single stage alkaline catalyst. In the case of mixed alcohol, a relatively smaller amount of ethyl esters was formed along with methyl esters. Acid value, viscosity, and cetane number of all the esters prepared from WFG were within the range of the ASTM standard. Esters obtained from WFG showed good performance as a lubricity additive.     

Channel-quality-based opportunistic scheduling with ARQ in multi-rate wireless networks: modeling and analysis

In this paper, we develop a novel framework for analyzing radio link level performance for opportunistic scheduling with automatic repeat request (ARQ)-based error control in multi-rate wireless networks. The multi-rate transmission is assumed to be achieved through adaptive modulation and coding (AMC) to adjust the transmission rate according to the channel condition. The residual error effect due to each AMC setting is counteracted by means of a limited persistence ARQ protocol. The novelty of the proposed analytical framework lies in the fact that we are able to derive complete statistics (in terms of probability mass function) for both short-term and long-term performance measures such as system throughput, per-flow throughput, inter-success delay under both uncorrelated and correlated wireless channels. These performance measures can also be obtained in case of non-identical channels for different users. Analytical results are validated through simulations and the impacts of channel behavior on the different radio link level performance metrics are investigated.     

Tuning radio resource in an overlay cognitive radio network for TCP: greed isn't good [Accepted from Open Call]

In this article we illustrate the performance of Transmission Control Protocol in an overlay cognitive radio network under dynamic spectrum access. We show that the performance of TCP in overlay CR networks that implement DSA to be quite different from its performance in conventional networks, which do not allow DSA. The key difference is that secondary users in an overlay CR network have to cope with a new type of loss called service interruption loss, due to the existence of primary users. We demonstrate on an NS2 simulation testbed the surprising result: Excessive radio resource usage leads to a decrease in aggregate TCP throughput. This behavior is in contrast to the behavior of TCP in conventional networks, where throughput increases monotonically with the available radio resource.     

Biodiesel production from mixtures of canola oil and used cooking oil

Used cooking oil (UCO) was mixed with canola oil at various ratios in order to make use of used cooking oil for production of biodiesel and also lower the cost of biodiesel production. Methyl and ethyl esters were prepared by means of KOH-catalyzed transesterification from the mixtures of both the oils. Water content, acid value and viscosity of most esters met ASTM standard except for ethyl esters prepared from used cooking oil. Canola oil content of at least 60% in the used cooking oil/canola oil feedstock is required in order to produce ethyl ester satisfying ASTM specifications. Although ethanolysis was proved to be more challenging, ethyl esters showed reduced crystallization temperature (−45.0 to −54.4 °C) as compared to methyl esters (−35.3 to −43.0 °C). A somewhat better low-temperature property of ester was observed at higher used cooking oil to canola oil ratio in spite of similar fatty acid compositions of both oils.     

Evaluating Esters Derived from Mustard Oil (<Emphasis Type="Italic">Sinapis alba</Emphasis>) as Potential Diesel Additives

Biodiesel was produced from mustard oil utilizing transesterification with methanol, ethanol, propanol, and butanol to evaluate the characteristics of mustard biodiesel as an additive to regular diesel. Mustard oil was transesterified with alcohol at 6:1 alcohol to oil molar ratio, using KOH as a catalyst at 1 wt%. The maximum ester content achieved by this method was only 66%. Distillation was then used to purify the ester, raising the ester content to 99.8%. Alternatively, mustard oil methyl ester (MME) can be mixed with esters derived from canola oil or soybean oil to achieve an ASTM quality biodiesel. Biodiesel derived from mustard showed great potential as lubricity additive for regular diesel fuel. With an addition of 1% MME, lubricity of diesel fuel was improved by 43.7%. It is also found that methyl ester is the best lubricity additive among all esters (methyl-, ethyl-, propyl-, and butyl-ester). MME can be used at −16 °C without freezing whereas monounsaturated compounds (oleic, eicosenoic, and erucic esters) largely present in esters derived from mustard oil can tolerate −42 to −58 °C. Monounsaturated esters derived from higher alcohols such as butyl alcohol demonstrated a superior low temperature tolerance (−58 °C) as compared to that derived from lower alcohol such as methyl alcohol (−42 °C).     

End-to-End Batch Transmission in a Multihop and Multirate Wireless Network: Latency, Reliability, and Throughput Analysis

This paper presents a novel Markov-based model for analyzing the end-to-end transmission of a batch of packets in a multihop wireless network using multirate transmission. The end-to-end reliability of this transmission (in terms of the number of packets delivered to the destination node) is controlled through different types of Automatic Repeat reQuest (ARQ)-based error control mechanisms implemented at each node. For a batch of packets, we derive complete statistics (i.e., probability mass function) for end-to-end latency and the number of packets successfully delivered to the destination node. Typical numerical results obtained from the model are validated by means of simulation. These results reveal the trade-off between end-to-end latency and end-to-end reliability, which would be an important issue in designing and engineering multihop wireless networks. Also, we demonstrate the usefulness of the proposed analytical model in predicting the latency and the reliability performances of TCP (Transmission Control Protocol) in a multihop wireless scenario.     

ORCA-MRT: an optimization-based approach for fair scheduling in multirate TDMA wireless networks

This paper presents an optimization-based approach to solve the wireless fair scheduling problem under a multirate time division multiple access (TDMA)-based medium access control (MAC) framework. By formulating the fair scheduling problem as an assignment problem, the authors propose the optimal radio channel allocation for multirate transmission (ORCA-MRT) algorithm for fair bandwidth allocation in wireless data networks that support MRT at the radio link level. The key feature of ORCA-MRT is that while allocating transmission rate to each flow fairly, it keeps the interaccess delay bounded under a certain limit. The authors investigate the performance of the proposed ORCA-MRT scheduler in comparison to another recently proposed multirate fair scheduling algorithm. They also propose two channel prediction models and perform extensive simulations to investigate the performance of ORCA-MRT for different system parameters such as channel state correlation, number of flows, etc.     

Performance Modeling and Analysis of a Class of ARQ Protocols in Multi-Hop Wireless Networks

This paper models and analyzes the performances of a class of ARQ (automatic repeat request) protocols in a multi-hop wireless data network. The performance metric here is the number of transmissions required for successful delivery of a packet over a multi-hop path. By using a discrete-time Markov model, the distribution for the total required number of transmissions is modeled as phase type distribution. The effects of different network parameters-such as packet error rate in each hop, maximum number of allowable retransmissions at each hop and retransmission probability at each hop-on the required total number of transmissions are investigated. The novelty of this model is that the probability mass function (pmf) for the number of transmissions required for successful end-to-end delivery of a packet can be easily obtained under different hop-level error control policies. Using the pmf, the tradeoff between transmission energy and percentage of data delivery (i.e., reliability) in a multi-hop path can be analyzed. The analytical model is validated by simulations. While the proposed analytical framework is general enough to capture the impact of any MAC (medium access control) mechanism at each hop, we specifically present typical performance results under IEEE 802.11 DCF (distributed coordination function) MAC     

Medium access control protocols for wireless mobile ad hoc networks: issues and approaches

In this article, a comprehensive survey of the medium access control (MAC) approaches for wireless mobile ad hoc networks is presented. The complexity in MAC design for wireless ad hoc networks arises due to node mobility, radio link vulnerability and the lack of central coordination. A series of studies on MAC design has been conducted in the literature to improve medium access performance in different aspects as identified by the different performance metrics. Tradeoffs among the different performance metrics (such as between throughput and fairness) dictate the design of a suitable MAC protocol. We compare the different proposed MAC approaches, identify their problems and discuss the possible remedies. The interactions among the MAC and the higher layer protocols such as routing and transport layer protocols are discussed and some interesting research issues are also identified. Copyright © 2003 John Wiley & Sons, Ltd.     

Comparative kinetics of transesterification for biodiesel production from palm oil and mustard oil

The kinetics of palm oil and mustard oil transesterification are compared. Transesterification of palm oil and mustard oil using KOH as a catalyst was performed at various reaction temperatures ranging from 40 to 60°C. The reaction steps are reversible and transesterification is favoured at elevated temperatures. The reaction step of triglyceride to diglyceride is the rate determining step (RDS) that controls kinetics of overall transesterification with activation energies of 30.2 and 26.8 kJ/mol for palm oil and mustard oil transesterification, respectively. It is found that percentage of saturated compounds play a vital role on transesterification kinetics. © 2011 Canadian Society for Chemical Engineering