Energy sustainability and environmental issues pose greater challenges on different primary energy sectors as the global energy demand increases and it is projected to further increase with an upsurge in population. On the other hand, energy sources from conventional fossil-based fuels are depleting, forcing explorations in challenging and difficult locations. As a result, the use of alternative fuels received dramatic consideration to substitute these conventional fuels, of which natural gas took the significant share. However, the share of natural-gas vehicles in the current vehicle market is quite small, and it is estimated to be below 5%. This paper reviews the current resource scenarios including proven and potential reserves, current production, and consumption, along with the fueling infrastructure, distribution, and storage. It also provides summary of the development of fuel-injection technologies aimed to enhance the performance of gas engines. More attention was also given to natural-gas engines and their limitations. Parameters affecting the performance and combustion of compressed natural gas (CNG) in spark-ignition (SI) engines are thoroughly assessed, among which compression ratio and injection timing play major roles in the optimization of CNG-fueled engines. Furthermore, different technologies that help close the performance gap between conventional liquid-fuel and natural-gas engines and future directions of the research are presented.

Natural Gas Engine Technologies: Challenges and Energy Sustainability Issue

This paper mainly evaluates the previously published fleet planning researches which primarily utilize operations research and computational intelligence based techniques. An intermodal fleet plann...

A review of fleet planning problems in single and multimodal transportation systems

A review on sustainable inventory routing

The ability of a supplier of liquefied natural gas (LNG) to deliver cargoes at desired times, while effectively managing a fleet of cryogenic vessels can significantly impact its profits. We investigate in this paper an LNG short-term delivery planning problem by considering mandatory cargoes as well as optional cargoes to select, along with the scheduling of a heterogeneous vessel fleet with controllable cruising speeds. Several technical constraints are accommodated including time windows, berth availability, bunkering restrictions, inventory, liquefaction terminal storage capacity, maximum waiting time, and planned maintenance restrictions. The objective is to maximize the net profit. We propose a mixed-integer programming formulation that includes a polynomial number of variables and constraints and accommodates all of the problem features. Also, we describe an optimization-based variable neighborhood search procedure that embeds the proposed compact formulation. To assess the quality of the generated solutions, we propose a second valid formulation with an exponential number of decision variables and we solve its linear programming relaxation using column generation. We provide the results of extensive computational results that were carried out on a set of large-scale set of realistic instances, with up to 62 vessels and 160 cargoes, provided by a major LNG producer. These results provide evidence that the proposed improvement procedure yields high-quality solutions.

Short-term planning of liquefied natural gas deliveries

The purpose of this study is to identify and evaluate supply chain strategies (SCSs) that drive financial performance to guide practitioners, especially in liquefied natural gas (LNG) networks, to review and adopt SCSs that drive competitiveness and value creation for investors.,Analytical hierarchy process (AHP) was deployed to prioritise SCSs according to their relative impact on financial performance in LNG networks. Interviews with experts were analysed using template analysis to establish latent drivers of financial performance specific to LNG networks.,Results support the significant role of SCSs in improving financial performance. Although findings prioritised collaborative strategy as the most important driver of financial performance in LNG networks, to fully optimise financial outcomes, all the SCSs should be implemented across LNG networks as no single strategy in isolation is a standalone driver of financial performance.,The AHP model provides a novel ranking for SCSs and measures to guide decision-makers. LNG practitioners may exploit the results to make informed decisions.,The study extends previous literature by proposing a framework and a new LNG empirical model that facilitates understanding of how SCSs contribute positively to financial performance and support practitioners in making strategic supply chain decisions.

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Supply chain strategies as drivers of financial performance in liquefied natural gas networks

We consider a strategic infrastructure and tanker fleet sizing problem in the liquefied natural gas business. The goal is to minimize long-term on-shore infrastructure and tanker investment cost combined with interrelated expected cost for operating the tanker fleet. A non-linear arc-based model and an exact solution method based on a set-partitioning formulation are developed. The latter approach allows very fast solution times. Computational results for a case study with a liner shipping company are presented, including an extensive sensitivity analysis to account for limited predictability of key parameter values, to analyze the solutions’ robustness and to derive basic decision rules.

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Anna Boleda Molas

Papers

The liquefied natural gas infrastructure and tanker fleet sizing problem