back period is less than three years [26].
The main switch in primary energy use or fuel use as it was previously mentioned was driven by economical aspects of it use. The main driver for fuel price in the future will not be supply and demand mechanism but more and more ecological aspects of fuel use. EU energy policy and environmental targets in energy sector represent the base for considering wider application of LNG in energy consumption in transitional period. The transport sector, as it was previously mentioned, represents one of the problematic issue since electrification of heavy-duty trucks in road traffic or marine transport is not an alternative in near future. Therefore, use of LNG represents alternative in transitional period towards sustainable energy society. The transport sector in the EU countries in 2009 was responsible for 20% of all emissions. One of the most obvious advantages of LNG as a fuel is visible if environmental considerations are taken into account [8,12,27,28,29,30,31,32,33]. The European Union encourages the development of alternative fuels to reduce carbon footprint [34]. Greenhouse gas emissions studies have been conducted during the lifecycle of diesel and LNG used in heavy road vehicles in Europe. The lifetime of the fuel is divided into three phases. The first phase is production, which also includes collecting and transportation, as well as diesel refining and LPG liquefaction, second phase is distribution, and the last phase is combustion. LNG liquefied at a large terminal produces about 10% less emissions than diesel fuel and LNG liquefied in a small plant produces around 3% less emissions than diesel fuel [8]. Apart from reducing CO2 emissions, SOX, NOX and particle emissions are also significantly reduced [35,36]. According to Kofod and Stephenson well to wheel GHG emissions from LNG trucks are around 19% lower than the ones from diesel truck and by using bio-LNG it’s possible to reduce GHG emissions up to 67% [37,38]. In China, the emissions were calculated based on the Tsinghua Fuel Lifecycle Analysis Model, a specifically designed fuel analysis instrument in China where the conclusion was that LNG powered vehicles have 5 to 10% less emissions than gasoline or diesel powered vehicles [9,27]. According to the research done by Song et al. usage of LNG trucks resulted in slight GHG reductions compared to a diesel trucks, estimated at approximately 8.0% based on the full life cycle [39]. Hao et al. said that one of the most effective strategies toward sustainable transportation is the promotion of natural gas vehicles with LNG as a very promising alternative. Compared to diesel vehicles, LNG vehicles tailpipe emissions can be more successfully controlled [40]. It is also important to notice that LNG powered heavy duty vehicles emit significantly less fine particles, which have a negative effect on human health, than conventional trucks [41]. Even though reductions of said greenhouse gasses are significant, climate benefits may be reduced or even delayed for decades due to loss of methane from gas supply chain. Methane impact on climate change is more than 25 times greater than same mass of CO2 over a 100-year period [42,43]. Thus, switch to LNG trucks may have negative impact on climate for next 200 years, even though usage of natural gas in other sectors may be beneficial at all time frames [44]. When switching from diesel to LNG heavy duty trucks, reduction in methane losses to the atmosphere may be needed to ensure climate benefits at all time frames. Until better data is available on magnitude of methane loss, impact of fuel switch is still uncertain [31]. Misra et al. report five tested technologies and results show that LNG trucks with the three-way catalyst have lower brake-specific NOx emissions. On the other hand, minimization of natural gas leakage into atmosphere during fueling and storing is crucial [45].
During history, LNG was misperceived as unsafe fuel since its liquefaction process in the first half of the 20th century was characterized by fatal accidents. But development of LNG industry after the 1950s and all scientific record show that LNG has been used for years without a major incident, so it can be considered as a relatively safe fuel [18,23]. As mentioned before, LNG has no color, is non-toxic or carcinogenic, and may explode only indoors at a concentration of 5% to 15% [46]. However, some special security measures are needed. LNG is cryogenic and dangerous if it comes into contact with skin or eyes, which is why it is imperative to use visor, gloves and other forms of protection when working with LNG. Compared to other fuels, LNG is very safe when all the regulations are followed including best business practices [47].
At this moment, there is no alternative powertrain or fuel that is economically attractive for long haul application, except for LNG trucks. Diesel fuel economy in traversed distance per equivalent of liter of diesel of LNG trucks with compression ignition is similar to diesel trucks, while LNG trucks with spark ignition have somewhat lower fuel economy (22% to 28% lower than diesel trucks). Hybridization of both LNG and diesel trucks improve fuel economy, but not significantly for long haul (3%–6%).
When it comes to CO2 emissions, LNG trucks can compete with diesel hybrid trucks and LNG trucks with compression ignition fare better than even fuel cell and battery electric trucks.
When it comes to breakeven price, as mentioned before, LNG trucks fare better than conventional diesel trucks and hybrids are not attractive option, except for diesel vehicles with a day cycles [48]. CNG and CNG hybrid trucks are also economically attractive options, but only for medium duty and urban applications [49].
LNG vehicles are increasingly being considered and used, in road, maritime, railway traffic. In the use of such vehicles, the most significant is China, which in 2017 had more than 230,000 LNG trucks and around 3000 filling stations (CNG and LNG). There was 540 percent increase of sales of LNG heavy trucks in first seven months of the 2017 which accounts around 39,000 new trucks. Also, China plans to increase a number of filling stations to around 12,000 stations by 2020. Locations and types of this filling stations are carefully chosen using premade studies [50]. That way LNG trucks would spend 40% of the total Chinese consumption of LNG [51,52,53,54]. Vehicle use of natural gas is considered to be a high priority by policy enacted in a year 2007 by National Development and Reform Commission of China [55]. US currently has 144 LNG filling stations across the country (76 public) and plans to build 38 new ones [56]. In Europe there are around 1500 LNG trucks along with around 100 LNG filling stations. Filling infrastructure is most developed in Northwest Europe (UK, Netherlands and Norway) [57]. In 2016, 81% of LNG-CNG filling stations in Europe were built in the Netherlands, the United Kingdom, and Spain. In the rest of the Europe, the building of LNG and LNG-CNG stations begun in 2014 [58,59,60,61,62]. Current number of filling stations can be seen on Figure 1 (yellow are filling stations that are planned or in construction) [63].
Within this paper, an analysis of the impact of LNG trucks on ecological and financial aspects for the European Union has been conducted. According to Kofod and Stephenson, well to wheel GHG emissions from LNG trucks are on average 19% less than the diesel ones. They claim that LNG trucks for 1 MJ of energy used produce 211.7 grams of CO2 equivalent (CO2eq), while a diesel trucks produce 262 grams of CO2 equivalent for 1 MJ of energy used [37]. These numbers were used in the calculation of annual GHG emission for one truck. The annual GHG emissions were obtained by multiplying annual mileage, average fuel consumption, and the heating value of one liter of diesel or one kilogram of LNG and said CO2 emission equivalent for 1 MJ of energy used. The Table 3 shows the selected parameters for the calculation of annual GHG emissions.
Annual GHG emissions per truck and emission reduction per truck depending on annual mileage expressed in tonnes of CO2eq are shown in the Table 4.
Due to the lack of data on the average annual mileage at EU level, several values ranging from 70,000 to 130,000 km are assumed for annual mileage. The value of 70,000 km was chosen by the author’s experience on the national market, while the value of 130,000 km was selected due to average annual mileage for Dutch distribution services [64]. Average fuel consumption and heating values were chosen based on author’s experience.
Over the past two years, around 300,000 new trucks are registered annually in the EU, considering that number, it was possible to calculate annual emission reduction presuming that some of the new diesel trucks would be replaced by LNG trucks [65]. An analysis was made based on several different LNG truck shares in the total number of new trucks in the EU with the assumption that all other trucks are diesel trucks. Proposed shares of LNG trucks were 5%, 10%, 15%, 20%, 25%, 30%, and 50%. GHG emissions reduction depending on the annual mileage of the vehicle and LNG truck share expressed in 1000 tonnes of CO2eq is shown in Table 5.
Emission reduction was obtained by multiplying the emission reduction per truck, total number of new trucks in the EU and LNG truck share.
As noted above, apart from the ecological, the financial impact of LNG trucks in the EU was also analyzed in this paper. Within this analysis, annual fuel costs per truck for five different diesel prices and five different LNG prices were calculated depending on the annual mileage. The annual fuel costs per truck cost was obtained by