1. STATE OF THE INDUSTRY
There are currently just under 100 LNG filling stations in Europe, several hundred in North America (Canada, USA, Mexico) and more than 1,500 in China. World car manufacturers are serially producing trucks designed to use LNG as fuel. Leaders in this field are: Iveco (Italy), Scania (Sweden), Shacman (China).
The first Russian manufacturer of powerful gas piston engines and CNG/LNG trucks is “KamAZ”. There are about 10 LNG vehicles in operation in Russia. LNG is used to a limited extent on railways in the United States and Russia. The Russian experience was recognized as successful; Russian Railways plans to significantly expand the fleet of gas engine locomotives.
According to various sources, about 200 large marine vessels with LNG engines and an unknown number of river vessels are operated in the world, and the number of such vessels is growing rapidly.
In Russia, at the moment, all refueling stations for a small number of LNG transport are of an experimental nature, where accounting is carried out using rather imperfect technologies. The only filling station with a submersible pump and a dispenser (manufactured by Vanzetti, Italy) recently closed after several years of trial operation.
2. PRECONDITIONS FOR TRANSITION OF VEHICLES TO LNG
Natural gas is highly energy efficient as a fuel. The calorific value of natural gas is about 48 MJ/kg, which is close to the calorific value of diesel fuel 51 MJ/kg. In the fuel tank of a vehicle, natural gas is stored in compressed up to 20 MPa (compressed natural gas, CNG) or liquefied (LNG) form.
Comparative analysis of different fuels sometimes uses different units of measure for quantity, which is confusing. The table below summarizes the characteristics of the fuels with “energy equivalent” ratios.
Thus, the use of natural gas in transport requires an increased volume of fuel tanks (cylinders). LNG provides a significantly higher efficiency of using the volume of fuel tanks compared to CNG, but still the volume is used 2 times less efficiently than when using diesel fuel. Nevertheless, this disadvantage is offset by the economic and environmental effect of the use of gas engine fuel, shown below.
2.2 Methods of using gas fuel in transport
There are several ways to ensure the operation of the engine on gas running.
Their features are summarized in the table below.
So, of the whole variety of options, items 2 and 5 of Table 2 are the most promising for large projects. Moreover, for cars and buses, these options are unambiguously associated with the acquisition of new equipment, and for river vessels an interesting option may be remotorization with replacement of diesel engines with gas piston. However, the lack of approval of the River Register can be a serious obstacle here, because currently, there are few types of gas piston engines approved for use on river vessels and suitable in terms of power.
In this regard, a possible option for ships may be the modernization of diesel engines on the gas-diesel principle, which in the case of ships with their almost constant operation mode will have a positive effect (a large percentage of diesel fuel can be replaced by gas).
There are two options for storing gas fuel on a vehicle: compressed natural gas (CNG) in high pressure cylinders and liquefied natural gas (LNG) in cryobanks.
In this review, we do not further consider CNG technology, since light vehicles make up a small share in large infrastructure projects, and city buses running on CNG are likely to start losing out to electric buses in terms of range and cost per kilometer in the near future.
Thus, the appearance of the transport under consideration is formed: it is a heavy truck, a large-capacity bus or a river passenger ship with a predicted and sufficiently large daily mileage, equipped with a gas piston or gas-diesel engine, with an LNG storage system (cryobanks).
2.3 Economic effect
The economic effect of the transition from the use of diesel fuel to LNG is formed due to the lower price of fuel. From the data given in Table 1, it follows that the fuel consumption in kg of LNG for the same mileage will be 12% lower than the consumption in liters of diesel fuel. This is in good agreement with statistics that say fuel consumption is reduced by 10-15%, depending on vehicle design and operating conditions.
2.4 Environmental impact
Much attention is now paid to minimizing greenhouse gas emissions and reducing the overall toxicity of engine exhaust.
According to European data, a CNG engine significantly reduces emissions compared to a diesel engine on a heavy truck in a combined cycle (“highway passing through small cities”):
… nitrogen oxides with 122 to 38 g / 100 km;
… CO2 from 93 to 82 kg / 100 km;
… substantially (almost up to 0) reduces soot emissions.
Thus, the main environmental effect is to reduce exhaust smoke and reduce greenhouse CO2 emissions by 10-12%.
It is important to note here that the use of LNG is associated with minor but important emissions of natural gas (methane), which itself is a greenhouse agent, about 25 times stronger than CO2. These emissions are due to bleeds from the fuel system and incomplete combustion of methane, and (see 3.1) there are also emissions from filling stations. The higher greenhouse activity of methane leads to the fact that a small amount of natural gas emissions can negate the effect of reducing CO2 emissions. Different engine designs have different methane emissions. Emissions of 10 kg of CO2 are equivalent to the emission of 400 g of methane per 100 km, or, in terms of fuel consumption, losses of 13 g per 1 kg of LNG (1.3%). Thus, it becomes extremely important to ensure the correct distribution, storage and refueling of LNG, so that the losses “from the LNG plant to the exhaust pipe” do not exceed this value.