Test drive alternatives: PART 2 - Cars
If you have the opportunity to fly over Western Siberia at night, through the window you will see a grotesque sight, reminiscent of the Kuwaiti desert after the withdrawal of Saddam's troops during the first war in Iraq. The landscape is littered with huge burning "torches", which is clear evidence that many Russian oil producers still consider natural gas a byproduct and unnecessary product in the process of finding oil fields ...
Experts believe that this waste will be stopped in the near future. For many years, natural gas was considered a surplus product and was burned or simply released into the atmosphere. It is estimated that so far Saudi Arabia alone has dumped or burned more than 450 million cubic meters of natural gas during oil production ...
At the same time, the process is reversed - most modern oil companies have been consuming natural gas for a long time, realizing the value of this product and its importance, which can only increase in the future. This view of things is especially characteristic of the United States, where, in contrast to the already depleted oil reserves, there are still large gas deposits. The latter circumstance is automatically reflected in the industrial infrastructure of a huge country, the work of which is unthinkable without cars, and even more so without large trucks and buses. There are more and more transport companies abroad that are upgrading the diesel engines of their truck fleets to work with both combined gas-diesel systems and only blue fuel. More and more ships are switching to natural gas.
Against the background of liquid fuel prices, the price of methane sounds fantastic, and many are beginning to doubt that there is a catch here - and with good reason. Considering that the energy content of a kilogram of methane is higher than that of a kilogram of gasoline, and that one liter (i.e., one cubic decimeter) of gasoline weighs less than a kilogram, anyone can conclude that a kilogram of methane contains much more energy than a liter of gasoline. It is clear that even without this apparent jumble of numbers and vague disparities, running a car running on natural gas or methane will cost you far less money than running a car running on gasoline.
But here is the classic big “BUT”… Why, since the “scam” is so big, almost no one in our country uses natural gas as a car fuel, and cars adapted for its use in Bulgaria are rarer. phenomenon from kangaroo to the pine Rhodope mountain? The answer to this perfectly normal question is not given by the fact that the gas industry around the world is developing at a frantic pace and is currently considered the safest alternative to liquid petroleum fuels. Hydrogen engine technology still has an uncertain future, the in-cylinder management of hydrogen engines is extremely difficult, and what is an economical method to extract pure hydrogen is not yet clear. Against this background, the future of methane is, to put it mildly, brilliant - especially since there are huge deposits of natural gas in politically safe countries, that new technologies (mentioned in the previous issue of cryogenic liquefaction and chemical conversion of natural gas into liquids) are becoming cheaper, while the price of classic hydrocarbon products are growing. Not to mention the fact that methane has every chance of becoming the main source of hydrogen for fuel cells of the future.
The real reason for the abandonment of hydrocarbon gases as automotive fuels is still low oil prices over the decades, which have pushed the development of automotive technology and related road transport infrastructure towards the provision of energy for gasoline and diesel engines. Against the background of this general trend, attempts to use gas fuel are rather sporadic and insignificant.
Even after the end of World War II, the shortage of liquid fuels in Germany led to the emergence of cars equipped with the simplest systems for using natural gas, which, although much more primitive, differ little from the systems used by Bulgarian taxis today. from gas cylinders and reducers. Gas fuels gained more importance during the two oil crises in 1973 and 1979-80, but even then we can only talk about short flashes that went almost unnoticed and did not lead to significant development in this area. For more than two decades since this most recent acute crisis, liquid fuel prices have remained consistently low, reaching absurdly low prices in 1986 and 1998 at $ 10 a barrel. It is clear that such a situation cannot have a stimulating effect on alternative types of gas fuel ...
At the beginning of the 11th century, the market situation is gradually but surely moving in a different direction. Since the 2001 September XNUMX terrorist attacks, there has been a gradual but steady upward trend in oil prices, which has continued to rise as a result of increased consumption by China and India and difficulties in finding new deposits. However, car companies are much more awkward in the direction of mass production of cars adapted to run on gaseous fuels. The reasons for this cumbersomeness can be found both in the inertia of thinking of the majority of consumers, accustomed to traditional liquid fuels (for Europeans, for example, diesel fuel remains the most realistic alternative to gasoline), and in the need for huge investments in pipeline infrastructure. and compressor stations. When this is added to the complex and expensive storage systems for fuel (especially compressed natural gas) in the cars themselves, the big picture starts to clear up.
On the other hand, gaseous fuel powerplants are becoming more diversified and follow the technology of their gasoline counterparts. Gas feeders already use the same sophisticated electronic components to inject fuel into the liquid (still rare) or gas phase. There are also more and more production vehicle models factory-set for monovalent gas supply or with the possibility of dual gas / petrol supply. Increasingly, another advantage of gaseous fuels is being realized - due to its chemical structure, gases are more fully oxidized, and the level of harmful emissions in the exhaust gases of cars using them is much lower.
A New Beginning
However, a breakthrough to the market will require targeted and direct financial incentives for end-users of natural gas as a vehicle fuel. To attract customers, methane sellers in Germany are already providing buyers of natural gas vehicles with special bonuses, the nature of which sometimes seems simply unbelievable - for example, the Hamburg gas distribution company reimburses individuals for the purchase of gas. cars from certain dealers for a period of one year. The only condition for the user is to stick the sponsor's advertising sticker on their car...
The reason why natural gas in Germany and Bulgaria (in both countries the vast majority of natural gas comes from Russia by pipeline) is much cheaper than other fuels, should be sought in a number of legal premises. The market price of gas is logically linked to the price of oil: as the price of oil increases, so does the price of natural gas, but the difference in prices for gasoline and gas for the end consumer is mainly due to lower taxation of natural gas. In Germany, for example, the price of gas is legally fixed until 2020, and the scheme of this “fixation” is as follows: during this period, the price of natural gas can grow along with the price of oil, but its proportional advantage over other energy sources must be maintained at constant level. It is clear that with such a regulated legal framework, low prices and the absence of any problems in the construction of "gas engines", the only problem for the growth of this market remains an undeveloped network of gas stations - in huge Germany, for example, there are only 300 such points, and in Bulgaria there are many. less.
The prospects for filling this infrastructural deficit look great at the moment - in Germany, the association of Erdgasmobil and the French oil giant TotalFinaElf intends to invest heavily in the construction of several thousand new gas stations, and in Bulgaria several companies have taken on a similar task. It is possible that soon the whole of Europe will use the same developed network of filling stations for natural and liquefied petroleum gas as consumers in Italy and the Netherlands - countries whose development in this area we told you about in the previous issue.
Honda Civic GX
At the 1997 Frankfurt Motor Show, Honda introduced the Civic GX, claiming it was the most environmentally friendly car in the world. It turned out that the ambitious statement of the Japanese is not just another marketing ploy, but the pure truth, which remains relevant to this day, and can be seen in practice in the latest edition of the Civic GX. The car is designed to run on natural gas only, and the engine is designed to take full advantage of the high octane rating of gaseous fuel. Not surprisingly, vehicles of this type today can offer exhaust emission levels lower than those required in a future Euro 5 European economy, or 90% lower than US ULEVs (Ultra Low Emission Vehicles). . The Honda engine runs extremely smoothly, and the high compression ratio of 12,5:1 compensates for the lower volumetric energy value of natural gas compared to gasoline. The 120-liter tank is made of composite material, and the equivalent gas consumption is 6,9 liters. Honda's famous VTEC variable valve timing system works well with the special properties of the fuel and further improves engine charge. Due to the lower burning rate of natural gas and the fact that the fuel is "dry" and does not have lubricating properties, the valve seats are made of special heat-resistant alloys. The pistons are also made of stronger materials, as the gas cannot cool the cylinders when it evaporates like gasoline.
The Honda GX hoses in the gas phase are injected with natural gas, which is 770 times larger than the equivalent amount of gasoline. The biggest technological challenge for Honda engineers was to create the right injectors to work in such conditions and prerequisites - in order to achieve optimal power, injectors must cope with the difficult task of simultaneously supplying the required amount of gas, for which, in principle, liquid gasoline is injected. This is a problem for all engines of this type, since the gas occupies a much larger volume, displaces some of the air and requires injection directly into the combustion chambers.
In the same 1997, Fiat also demonstrated a similar Honda GX model. The "bivalent" version of Marea can use two types of fuel - gasoline and natural gas, and the gas is pumped by a second, completely independent fuel system. The engine always starts on liquid fuel and then automatically switches to gas. The 1,6-liter engine has a power of 93 hp. with gas fuel and 103 hp. With. when using gasoline. In principle, the engine runs mainly on gas, except when the latter runs out or the driver has a clear desire to use gasoline. Unfortunately, the "dual nature" of bivalent energy does not allow full use of the advantages of high-octane natural gas. Fiat is currently producing a Mulipla version with this type of PSU.
Over time, similar models appeared in the range of Opel (Astra and Zafira Bi Fuel for LPG and CNG versions), PSA (Peugeot 406 LPG and Citroen Xantia LPG) and VW (Golf Bifuel). Volvo is considered a classic in this area, producing variants of the S60, V70 and S80, capable of running on natural gas as well as biogas and LPG. All of these vehicles are equipped with gas injection systems using special nozzles, electronically controlled technological processes and fuel-compatible mechanical components such as valves and pistons. CNG fuel tanks are designed to withstand a pressure of 700 bar, although the gas itself is stored there at a pressure of no more than 200 bar.
BMW
BMW is a well-known advocate of sustainable fuels and has been developing various powertrains for vehicles with alternative sources for many years. Back in the early 90s, the Bavarian company created models of the 316g and 518g series, which use natural gas as fuel. In its latest developments, the company decided to experiment with fundamentally new technologies and, together with the German refrigeration group Linde, the Aral oil company and the energy company E.ON Energy, developed a project for the use of liquefied gases. The project is developing in two directions: the first is the development of liquefied hydrogen supplies, and the second is the use of liquefied natural gas. The use of liquefied hydrogen is still considered a promising technology, which we will talk about later, but the system for storing and using liquefied natural gas is quite real and can be put into practice in the automotive industry in the next few years.
At the same time, natural gas is cooled to a temperature of -161 degrees and condenses at a pressure of 6-10 bar, while passing into the liquid phase. The tank is much more compact and lighter in comparison with compressed gas cylinders and is practically a cryogenic thermos made of super-insulating materials. Thanks to modern Linde technology, despite the very thin and light tank walls, liquid methane can be stored in this state for two weeks without problems, even in hot weather and without the need for refrigeration. The first LNG filling station, in the construction of which € 400 was invested, is already operating in Munich.
Combustion processes in gaseous fuel engines
As already mentioned, natural gas contains mainly methane, and liquefied petroleum gas - propane and butane in proportions that depend on the season. As molecular weight increases, the knock resistance of paraffinic (straight-chain) hydrocarbon compounds such as methane, ethane, and propane decreases, the molecules break apart more easily, and more peroxides accumulate. Thus, diesel engines use diesel fuel rather than gasoline, since the autoignition temperature is lower in the former case.
Methane has the highest hydrogen / carbon ratio of all hydrocarbons, which in practice means that for the same weight, methane has the highest energy value among hydrocarbons. Explaining this fact is complex and requires some knowledge of the chemistry and energy of relationships, so we will not deal with this. Suffice it to say that the stable methane molecule provides an octane number of about 130.
For this reason, the combustion rate of methane is much lower than that of gasoline, small molecules allow methane to burn more completely, and its gaseous state leads to less leaching of oil from the cylinder walls in cold engines compared to gasoline mixtures. ... Propane, in turn, has an octane rating of 112, which is still higher than most gasolines. Poor propane-air mixtures burn at a lower temperature than gasoline, but rich ones can lead to thermal overload of the engine, since propane does not have the cooling properties of gasoline due to its entry into the cylinders in gaseous form.
This problem has already been solved with the use of systems with direct injection of liquid propane. Because propane liquefies easily, it's easy to build a system to store it in a car, and there's no need to heat the intake manifolds because propane doesn't condense like gasoline does. This in turn improves the thermodynamic efficiency of the engine, where it is safe to use thermostats that maintain a lower coolant temperature. The only significant disadvantage of gaseous fuels is the fact that neither methane nor propane has a lubricating effect on exhaust valves, so experts say it is a "dry fuel" that is good for piston rings but bad for valves. You can't rely on gases to deliver most of the additives to the engine's cylinders, but engines running on these fuels don't need as many additives as gasoline engines. Mixture control is a very important factor in gas engines, as rich mixtures result in higher exhaust gas temperatures and valve overload, while poor mixtures create a problem by lowering an already low combustion rate, which again is a prerequisite for thermal valve overload. . The compression ratio in propane engines can easily be increased by two or three units, and in methane - even more. The resulting increase in nitrogen oxides is offset by lower emissions overall. The optimal propane mixture is slightly "poorer" - 15,5:1 (air to fuel) versus 14,7:1 for gasoline, and this is taken into account when designing evaporators, metering devices or injection systems. Because both propane and methane are gases, engines do not need to richen mixtures during cold starts or acceleration.
Ignition overtake angle is calculated on a different curve than gasoline engines - at low rpm, ignition overtake should be higher due to slower combustion of methane and propane, but at high speeds, gasoline engines need more increase. mixture (the combustion rate of gasoline is reduced due to the short time of pre-flame reactions - that is, the formation of peroxides). That is why the electronic ignition control systems of gas engines have a completely different algorithm.
Methane and propane also increase the requirements for high voltage spark plug electrodes - a "drier" mixture is "harder" to pierce than a spark because it is a less conductive electrolyte. Therefore, the distance between the electrodes of spark plugs suitable for such engines is usually different, the voltage is higher, and in general the issue of spark plugs is more complex and subtle than for gasoline engines. Lambda probes are used in the most modern gas engines for optimum mixture dosing in terms of quality. Having ignition systems on two separate curves is especially important for vehicles equipped with bivalent systems (for natural gas and gasoline), since the sparse network of natural gas filling points often requires the forced use of gasoline.
The optimum compression ratio of natural gas is about 16:1, and the ideal air-fuel ratio is 16,5:1. will lose about 15% of its potential power. When using natural gas, the amount of carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gases is reduced by 90%, and nitrogen oxides (NOx) by about 70% compared to conventional gasoline engine emissions. The oil change interval for gas engines is usually doubled.
Gas-diesel
In the past few years, dual-fuel fuel delivery systems have become increasingly popular. I hasten to note that we are not talking about "bivalent" engines running alternately on gas or gasoline and having spark plugs, but about special diesel-gas systems in which part of the diesel fuel is replaced by natural gas supplied by a separate power system. This technology is based on standard diesel engines.
The principle of operation is based on the fact that methane has a self-ignition temperature above 600 degrees - i.e. above a temperature of approximately 400-500 degrees at the end of the diesel engine compression cycle. This, in turn, means that the methane-air mixture does not ignite on its own when compressed in the cylinders, and the injected diesel fuel, which ignites at about 350 degrees, is used as a kind of spark plug. The system could run entirely on methane, but in this case it would be necessary to install an electrical system and a spark plug. Typically the percentage of methane increases with load, at idle the car runs on diesel, and at high load the methane/diesel ratio reaches 9/1. These proportions can also be changed according to the preliminary program.
Some companies produce diesel engines with the so-called. "Micropilot" power systems, in which the role of the diesel system is limited to the injection of a small amount of fuel needed only to ignite methane. Therefore, these engines cannot operate autonomously on diesel and are usually used in industrial vehicles, cars, buses and ships, where costly re-equipment is economically justified - after its wear, this leads to significant savings, engine life. increases significantly, and emissions of harmful gases are significantly reduced. Micropilot machines can operate on both liquefied and compressed natural gas.
Types of systems used for additional installation
The variety of gas supply systems for gaseous fuels is constantly growing. In principle, species can be divided into several types. When propane and methane are used, these are blended atmospheric pressure systems, gas phase injection systems, and liquid phase injection systems. From a technical point of view, propane-butane injection systems can be divided into several generations:
The first generation are systems without electronic control, in which the gas is mixed in a simple mixer. These are usually equipped with old carburetor engines.
The second generation is an injection with one nozzle, an analog lambda probe and a three-way catalyst.
The third generation is an injection with one or more nozzles (one per cylinder), with microprocessor control and the presence of both a self-learning program and a self-diagnosis code table.
The fourth generation is sequential (cylindrical) injection depending on the position of the piston, with the number of nozzles equal to the number of cylinders, and with feedback through a lambda probe.
Fifth generation - multi-point sequential injection with feedback and communication with a microprocessor to control gasoline injection.
In the most modern systems, the "gas" computer makes full use of the data from the main microprocessor to control the parameters of the gasoline engine, including injection time. Data transmission and control is also fully linked to the main petrol program, which avoids the need to create entire XNUMXD gas injection maps for each car model - the smart device simply reads the programs from the petrol processor. and adapts them to gas injection.
