Natural gas fuel and greenhouse gas emissions in trucks and ships

Abstract

Natural gas is a transport fuel which may help reduce greenhouse gas emissions in shipping and trucks. However, there is some disagreement regarding the potential for natural gas to provide significant improvements relative to current ships and trucks. In 2015, road freight represented ~7% of global energy related CO 2 emissions, with international shipping representing ~2.6% of global emissions. These emissions are also expected to grow, with some estimates suggesting road freight emission growing by a third, and shipping emissions growing by between 50% and 250% from 2012 to 2050, making absolute emissions reductions challenging. In addition, reducing emissions in ships and trucks has proved technically difficult given the relatively long distances that ships and trucks travel.This paper documents a systematic review of literature detailing well-to-wheel/wake greenhouse gas emissions and economic costs in moving from diesel and heavy fuel oil to natural gas as a fuel for trucks and ships. The review found a number of important issues for greenhouse gas reduction. First, moderate greenhouse gas reductions of 10% were found when switching to natural gas from heavy fuel oil in shipping when comparing the lowest estimates. Comparing lowest well-towheel greenhouse gas emissions estimates for trucks, the benefit of switching to natural gas fuel is approximately a 16% reduction in greenhouse gas emissions. However, these emissions are highly variable, driven particularly by methane emissions in exhaust gas. Given this, in the worst cases natural gas ships and trucks emit more greenhouse gasses than the diesel trucks and heavy fuel oil ships that they would replace. It appears relatively cost effective to switch to natural gas as a transport fuel in ships and trucks. However, the limited emissions reduction potential raises questions for the ongoing role of natural gas to reduce greenhouse gas emissions in line with the challenging greenhouse gas reduction targets emerging in the transport sector.

Environmental Protection and Energy Efficiency Improvement by using Marine Alternative fuels in Maritime Transportation

“…Specific Pilot Fuel Consumption at CSR (g/kWh) 6.1 The values of emissions factors of CO , NOx, SO X , PM and CO for two-stroke diesel engine operated by Marine Diesel oil (MDO) are g/kWh, 13.6 g/kWh, 3.57 g/kWh, 0.44 g/ kWh and 0.35 g/kWh, respectively. While Emission factors of CO 2 , NOx, SOx, PM and CO for the natural gas engine are 355 g/kWh, 2.16 g/kWh, 0 g/kWh, 0.03 g/ kWh and 0.3 g/kWh, respectively (Banawan et al 2010b;Seddiek and Elgohary 2014;Speirs et al 2020). Dual fuel engine's emission factors can be calculated from that of marine diesel oil and natural gas engines by taking the percent of each one into account.…”

Does Size Matter? The Influence of Size, Load Factor, Range Autonomy, and Application Type on the Life Cycle Assessment of Current and Future Medium- and Heavy-Duty Vehicles

“…VECTO does not come with engine maps for CNG engines. Hence, current efficiencies for CNG engines are set to be 19% lower than what is obtained from the calibration of ICEV-d trucks, corresponding to the performance of a spark-ignition CNG engine, according to ref . By 2030, the engine is assumed to be of compression-ignition type to achieve better performances.…”

“…By 2030, the engine is assumed to be of compression-ignition type to achieve better performances. It reflects the use of a dual CNG-diesel fuel injection system, which reduces the relative difference in thermal efficiency compared to a diesel engine to 14%, as reported by ref . After 2030, the efficiency of the CNG engine converges with that of a diesel engine to reach equivalent performances by 2050, as also suggested by ref .…”

“…Finally, pump-to-tank leaks when filling with gaseous fuels are also considered. They are accounted for as a fraction of the fuel input being directly emitted as methane, with a median value of 0.4%, as reported by ref .…”

A Study on Performance and Emission Characteristics of Direct Injection Natural Gas Engine

“…In the view of fact that the raw component in natural gas is methane, which have a low carbon/hydrogen (C/H) ratio, the COx emissions is reduced in the combustion products [4]. The natural gas vehicles are demonstrated to reduce the greenhouse gas emissions compared to gasoline or diesel fuel transportations [5,6].…”