Elsevier

Applied Energy

Volume 242, 15 May 2019, Pages 1738-1752
Applied Energy

Life cycle (well-to-wheel) energy and environmental assessment of natural gas as transportation fuel in Pakistan

https://doi.org/10.1016/j.apenergy.2019.03.196Get rights and content

Highlights

  • Well-to-Wheels analysis of energy consumptions and GHG emissions.

  • Analysis covers 25 combinations of automotive fuel and matching powertrain systems.

  • Well-to-Tank stage analysis conducted using GREET model.

  • Tank-to-Wheel stage analysis conducted using AVL Cruise vehicle simulator.

  • A 20% reduction of GHG emissions may be realized by switching from gasoline to NGV.

Abstract

Consumers and organizations worldwide are searching for low-carbon alternatives to conventional gasoline and diesel vehicles to reduce greenhouse gas (GHG) emissions and their impact on the environment. Natural gas as an alternative transportation fuel has made significant inroads in the light and heavy duty vehicles market over the last fifteen years. In a sustainable development view, both vehicle emissions and energy supply chain analysis from well-to-wheel must be addressed. The aim of this research is to provide a Well-to-Wheel (WtW) assessment of energy consumptions and GHG emissions for 25 combinations of automotive fuel and matching powertrain systems, with a special focus on the natural gas pathways. Although several well-to-wheel studies available in literature are comprehensive in relation to developed countries’ conditions, it is problematic to apply the results to developing countries fuel markets, since the local fuel conditions and respective vehicle powertrain technologies are considerably different. This study deal with a comparative well-to-wheel analysis of natural gas, diesel and gasoline fuels looking at the Pakistanis situation but the models and approaches for this study can be applied to other countries having similar characteristics, as long as all the assumptions are well defined and modified to find a substitute automotive energy source and establish an energy policy in a specific region. The well-to-tank step was made using the GREET model, developed by the U.S. Argonne National Laboratory while tank-to-wheel analysis was performed using AVL Cruise, a commercially-available backward vehicle simulator. Later both stages were integrated in a well-to-wheel stage where relevant indexes were proposed and discussed. The results indicate that natural gas vehicles are 5–17% and 23–36% less fuel efficient, depending on the engine technology employed as compared to gasoline and diesel powertrain, respectively. Natural gas appears as an environmental efficient pathway regarding GHG emissions, especially compared to gasoline. In addition, using 20-year GWPs instead of 100-year GWPs increases WtW GHG emissions by 19–26% for natural gas pathways.

Introduction

The Paris Agreement – the first-ever universal, legally binding global climate deal – was adopted by 195 countries at the Paris Climate Conference (COP21) in December 2015. The Paris Agreement requires all Parties to put forward their best efforts through “nationally determined contributions” (NDCs) to greatly reduce greenhouse gas (GHG) emissions. Being the world’s 6th most populated nation, its energy requirement establishes Pakistan as a major contributor of GHG emissions; therefore, the reduction of the GHG emissions in Pakistan has attracted substantial local attention. The energy consumption of the road transportation sector accounts for 33% of the total energy consumption in Pakistan [1] and is responsible for a significant share (around 25%) of GHG emissions nationwide [2]. Therefore the reduction of GHG emissions in the transportation sector is a top priority of the government [3].

Emissions and energy consumption are often measured at the point of use. This does not, however, account for the overall emissions and energy consumption. To evaluate the impact of fuels and energy carriers the whole supply chain has to be considered [4]. To evaluate and assess the energy consumption, emissions, and economic effects of automotive fuels and vehicle technologies, a holistic or comprehensive approach has to be considered. The approach, often referred to as life cycle approach, or life cycle assessment (LCA), which must include all the steps required to produce a fuel, to manufacture a vehicle, and to operate and maintain the vehicle throughout its lifetime including disposal and recycling at the conclusion of its life cycle. A lifecycle analysis of energy consumed and emissions generated is especially important for technologies that employ fuels with different primary energy sources and fuel production processes. A typical life cycle of a vehicle technology is shown in Fig. 1. The life cycle can be classified into two major categories: the fuel cycle and the vehicle cycle. The fuel lifecycle analysis, also known as well-to-wheel analysis is vital for selecting vehicle fuels and technologies for the future.

The well-to-wheel analysis indicates the study of the energy use and GHG emissions in the production of the fuel and its use in the vehicle or engine, hereinafter called WtW analysis. Compared to Life Cycle Assessment (LCA) a WtW analysis can have the same system boundaries but does not consider energy or emissions involved in the construction of the facilities, the vehicles, consumption of other materials, water, and end of life disposal [5]. The whole WtW cycle is comprised of two independent stages, as shown in Fig. 2. These include (i) a Well-to-Tank (WtT) stage, which includes the recovery or production of the feedstock for the fuel, transportation and storage of the energy source through conversion of the feedstock to the fuel and the subsequent transportation, storage, and distribution of the fuel to the vehicle tank, and (ii) a Tank-to-Wheel (TtW) stage, which refers to the vehicle in utilizing the fuel for traveling purposes throughout its lifetime.

The rest of this paper is structured as follows: Section 2 reviews the existing literature. Section 3 defines the key assumptions and parameters used in well-to-wheel analysis including functional unit, GHG coefficients, fuel pathways, and methane slip/leakage and vehicle technologies. Section 4 describes the research methodology and data. The results and discussion are reported in Section 5. A comparative analysis of this study with previous studies is presented in Section 6. Section 7 concludes the outcomes of the study.

Section snippets

Review of the state-of-the-art

Many variations of WtW studies [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18] have been proposed in the literature to capture different aspects of the fuel life-cycle of transportation fuels for various propulsion in different regions of the world. However WtW studies on CNG vehicles haven’t got much academic interest and only a few analyses have been conducted targeting the CNG fuel, with often varied and even contrasting results. In this section, we have presented a

Methodology and data

As mentioned above the WtT cycle consist of two stages i.e (i) WtT stage, and (ii) TtW stage. The WtT stage of study has been covered in part-1 [33] of this two-part study. In this paper, the Well-to-Tank (WtT) results observed in part-1 [33] are combined with the TtW (Tank-to-Wheel) results reported in this present paper to provide the comprehensive WtW (Well-to-Wheel) results for the operation of conventional and CNG passenger vehicle drivetrains specific to Pakistan.

Tank-to-Wheel phase of

Key assumptions and parameters

Following are key parameters and assumptions used in this study:

Results and discussion

In this study, a WtW analysis on 25 combinations of automotive fuel and matching powertrain systems available in Pakistan was conducted.

Comparison with other studies

The WtW energy use and GHG emissions results of various studies and the present study are represented in Fig. 12. Generally speaking, detailed comparisons cannot be made among the findings of WtW analysis of similar fuel due to different methods of modeling, types of input data used, system boundaries, engine parameters etc. Different methodologies and assumptions in different studies make scenario comparison difficult or impossible. Therefore the comparison of absolute results from these

Conclusions

The present study has been conducted to provide detailed WtW assessment of energy consumptions and GHG emissions of natural gas, gasoline and diesel fuel pathways at the Pakistan and energy importing developing countries levels. The results of the present study can be used as an input to the strategic decision-making process for future transport energy policy and also to identify key areas of interest for further technology research and development of the Pakistan transport system. Furthermore,

Acknowledgements

The authors are thankful to AVL List GmbH for providing licenses to AVL CRUISE under AST-University Partnership Program with University of Engineering & Technology, Peshawar, Pakistan.

References (60)

  • K. Morganti et al.

    Synergistic engine-fuel technologies for light-duty vehicles: fuel economy and greenhouse gas emissions

    Appl Energy

    (2017)
  • F. Orsi et al.

    A multi-dimensional well-to-wheels analysis of passenger vehicles in different regions: primary energy consumption, CO2 emissions, and economic cost

    Appl Energy

    (2016)
  • J. Hofmann et al.

    Assessment of electrical vehicles as a successful driver for reducing CO2 emissions in China

    Appl Energy

    (2016)
  • X. Yuan et al.

    Energy and environmental impact of battery electric vehicle range in China

    Appl Energy

    (2015)
  • Y. Xu et al.

    Assessment of alternative fuel and powertrain transit bus options using real-world operations data: life-cycle fuel and emissions modeling

    Appl Energy

    (2015)
  • M.G. Waller et al.

    Current and theoretical maximum well-to-wheels exergy efficiency of options to power vehicles with natural gas

    Appl Energy

    (2014)
  • M.F. Torchio et al.

    Energy, environmental and economic comparison of different powertrain/fuel options using well-to-wheels assessment, energy and external costs–European market analysis

    Energy

    (2010)
  • M. Yazdanie et al.

    A comparative analysis of well-to-wheel primary energy demand and greenhouse gas emissions for the operation of alternative and conventional vehicles in Switzerland, considering various energy carrier production pathways

    J Power Sources

    (2014)
  • J. Ally et al.

    Life-cycle assessment of diesel, natural gas and hydrogen fuel cell bus transportation systems

    J Power Sources

    (2007)
  • L. Rose et al.

    A comparative life cycle assessment of diesel and compressed natural gas powered refuse collection vehicles in a Canadian city

    Energy Policy

    (2013)
  • X. Ou et al.

    Alternative fuel buses currently in use in China: life-cycle fossil energy use, GHG emissions and policy recommendations

    Energy Policy

    (2010)
  • V. Patil et al.

    Life-cycle analysis of energy and greenhouse gas emissions of automotive fuels in India: Part 2–Well-to-wheels analysis

    Energy

    (2016)
  • S.J. Curran et al.

    Well-to-wheel analysis of direct and indirect use of natural gas in passenger vehicles

    Energy

    (2014)
  • M.I. Khan

    Comparative Well-to-Tank energy use and greenhouse gas assessment of natural gas as a transportation fuel in Pakistan

    Energy for Sustainable Development

    (2018)
  • B. Wahono et al.

    Analysis of range extender electric vehicle performance using vehicle simulator

    Energy Procedia

    (2015)
  • M.I. Khan et al.

    Technical overview of compressed natural gas (CNG) as a transportation fuel

    Renew Sustain Energy Rev

    (2015)
  • A.H. Kakaee et al.

    Research and development of natural-gas fueled engines in Iran

    Renew Sustain Energy Rev

    (2013)
  • D.R. Johnson et al.

    Greenhouse gas emissions and fuel efficiency of in-use high horsepower diesel, dual fuel, and natural gas engines for unconventional well development

    Appl Energy

    (2017)
  • M.M. Rahman et al.

    Well-to-wheel life cycle assessment of transportation fuels derived from different North American conventional crudes

    Appl Energy

    (2015)
  • W. Shen et al.

    Well-to-wheels life-cycle analysis of alternative fuels and vehicle technologies in China

    Energy Policy

    (2012)
  • Cited by (0)

    View full text