RCGI intends to improve large combustion engines for vessels and thermoelectric plants

There is still room to improve combustion processes in large-sized natural gas-fuelled engines, also in the sense of minimizing methane slip.

Developing technologies to improve combustion processes and minimizing methane slip in large natural gas-fuelled engines is the major goal of the project Advanced Combustion System using diesel and natural gas blends for Internal Combustion Engines applications minimizing methane slip, which integrates the project portfolio of the Research Centre for Gas Innovation (RCGI).

Coordinated by Professor Guenther C. Krieger Filho, from the Escola Politécnica (Engineering School) of the USP, the project focuses on engines generally used by vessels (including those carrying methane) and thermoelectric plants. “They are engines fuelled by diesel and bunker oil, which are heavy oils, and we want engines to operate with natural gas, which emits less CO2. Natural gas is a fuel which tends to detonate in internal combustion engines, though. If we make the same engines operate with natural gas, we will probably not achieve the power they would have with diesel,” advances Krieger.

He explains that large engines that use natural gas, instead of having an ignition spark plug, count on a pilot flame started by a diesel spray in a pre-combustion chamber. “Diesel is injected and, due to this pre-chamber temperature and pressure, an initial flame is formed, ensuring a more stable operation to the engine, due to the lack of detonation, or due to the lack of misfiring (failure in combustion cycles).”

The idea is to replace diesel or the heavy oil that moves the engine with natural gas, while keeping the pre-combustion chamber with diesel spray ignition. The researchers want to know how to control the two flames (that of gas in the main chamber and that of diesel in the pre-chamber), to have the expected power and stability in combustion. For this, they are building a combustion chamber with optical access (quartz windows) to study what occurs during the burning process with natural gas.

“There is a main chamber, filled with natural gas and air, with a small chamber in it, which we are going to fill with natural gas and air, and then inject a diesel spray inside it. Owing to the pressure and temperature, the diesel makes this ignition feasible. This mix with the gas and the air inside it starts to burn and the flame spreads, ensuring the combustion process.”

According to Krieger, there are already large engines fuelled with natural gas, but there is still room to improve the combustion processes, for example to minimize the methane slip, which occurs when the combustion process does not develop completely. “In one of the existing technologies, which does not penalise the engine power, natural gas is injected when the piston is at the end of the compressive process. However, in case it does not burn, when the exhaust valve opens, natural gas leaks from the cylinder and enters the atmosphere. This slip is what we want to avoid, since natural gas is basically composed of methane.”

The engineer remarks that, in this case, failures in the combustion system have a high cost to the environment. “Methane is 20 times more harmful to the environment as carbon dioxide. If it does not burn, that is, if this combustion cycle does not work and CH4 escapes into the atmosphere, it causes damages in terms of emissions. The technology we are studying ensures high power and safety with the engine operating with natural gas alone, and not only in the dual fuel system.”

In the first stage of the project, a combustion chamber (a vessel pressurised up to 100 bar) will be develop, with optical access allowing the passage of laser beams, so that the team can study the process of forming the ignition mix and the combustion process. “The idea is to deliver experimental data of high scientific value, obtained from ‘state-of-the-art’ combustion diagnosis technology. These data will help solve the problems that may occur in this combustion process.”

In the second stage, Krieger and his team, composed of three other engineers, will acquire a single cylinder, dual fuel (gas and diesel), research engine with optical access. “Its characteristics are close to those of a real engine. We can place a laser beam at the window and, when it is reflected or altered, we manage to understand the combustion process. It is then possible to make some measurements: the velocity field of the gases, where the drops of this diesel spray are from, their diameter and speed. We will be able to identify where the region of the flame is and how it was formed. All these data will feed a computational model, which we intend to extrapolate to large engines.”

Krieger states that, with the recent standards that provide increasingly lower emission rates for greenhouse gases (GHGs), large engines will have to turn to natural gas. “The process under study has to be better than that provided by the standards, since they are going to be increasingly stricter. And natural gas is a great alternative for reducing emissions.”

The whole experimental part will be developed at the Laboratory of Advanced Combustion Diagnosis; its assembling is the goal of one of the projects conducted within the RCGI ambit. “The laboratory will be a multi-user centre, that is, research teams having a demand for using it will be able to do it, even not being connected to the RCGI or to Poli, as long as they present their proposal and this is also interesting to us. We want more people to use it, the demands to appear.” The laboratory is being equipped with different types of laser diagnostics, which allow accurate analyses of the combustion processes studied.

Researchers study hybrid systems for generation of energy in ships

The Project is from the Research Centre for Gas Innovation (RCGI) and has the ultimate aim of replacing fossil fuels by electricity and natural gas.

Engineers from the Research Centre for Gas Innovation (RCGI) study the development of hybrid power systems for ships. The aim of having a hybrid system for ships is directly related to saving fuel. One of the immediate consequences thereof is the reduction of emissions, as the use of batteries allows the use of smaller motors, always operating under conditions that are close to those of greatest efficiency. In addition, at a second moment, the primary source used would be natural gas – a fuel considered as a “transition fuel”, having a cleaner burning process than other fossils currently used in naval applications.

The project co-ordinator, Bruno Souza Carmo, who is a professor at the Polytechnic School of the University of São Paulo (Poli-USP), explains that the project includes the application of hybrid systems in three different types of seagoing vessels: escort tugs, offshore supply vessels (that give support to prospection oil rigs, being responsible for the transport of supplies and provision of assistance to maritime units) and shuttle tankers (cargo ships that are designed for the transport of petroleum from an offshore oilfield). These last vessels work with what is known as dynamic positioning (DP): they need to maintain a stable position on carrying out loading and offloading operations, regardless of the conditions of the sea and wind.

“The project is divided into three phases. The first phase is that of appraisal of the implementation of the hybrid systems in ships with the use of batteries for energy storage, together with the traditional bunker oils that currently move the ships. This first phase would take about two years.”

According to the engineer, the batteries used depend on the type of ship and also on its function. “One of the technologies we shall be using is that of lithium ion batteries. However, depending on the type of application and the kind of ship, the type of battery to be used could be different. We do not yet know the power of the battery we shall need for each type of ship, or the size thereof. What we do know is that more than one battery shall be required: these shall be battery benches”.

He also explains that there is significant concern about security issues, as the use of batteries on ships is a fairly new development. “It shall be necessary, therefore, to design places where these batteries shall be kept, with special attention being given to ventilation, for example, as they heat up. One of the engineers on our team shall be taking care exclusively of the security issue.”

The fuel saving thus made available through the use of batteries depends on the vessel considered. In the case of an escort tug, according to the engineer, the saving is between 20% and 30%. Mr Carmo adds that so far there is no regulation in the world for hybrids in terms of security aspects, specification of components and other factors. “This is all still being devised, still being studied.”

Check out the project´s 7 page

Natural Gas – In the second phase of the Project, known as Hybrid Systems based on Natural Gas, the aim is to include natural gas as a fuel for the ships. There are already ships running on natural gas (not many, but they do exist). These are mainly ferry boats for passenger transport. “These are widely used in Canada and in Scandinavia, in environmental protection areas, where emissions have to be lower”, Mr Carmo reveals.

Apart from reducing the emission of pollutants, there is another factor to motivate the use of natural gas as fuel in the vessels studied: that of making use of the gas that evaporates from the ships transporting natural liquefied natural gas (LNG). “These ships have enormous spherical tanks for the transport of liquefied natural gas. The natural gas evaporates as the transportation process occurs, as it is impossible to thermally isolate this fuel entirely. So what is done with the gas that evaporates? Nothing, the gas is lost. Whoever buys the LNG just wants the liquid, not the gas. So the idea is that of using it as fuel for the ship itself.”

The third and most ambitious phase of the Project is the use of fuel cells to get the ships moving. “At this point, we need to see which is most feasible: that of having a re-formation system for natural gas vapour on board, to transform the natural gas into hydrogen that shall be used in the cells, or if, four or five years from now, we shall already master a developed technology to make these cells operate on natural gas, something that we call dry re-formation. There is another project at the RCGI, co-ordinated by professor Fábio Coral Fonseca, of the Institute for Energy and Nuclear Research (Ipen), which is trying to develop this technology. Then we would have the best of both worlds: a cleaner type of fuel being used in a manner which is more efficient than combustion, as the fuel cell, all things considered, generates electricity.”

Apart from Mr Carmo, five more engineers are part of the Project, being responsible for specific areas: security (risk analysis), energy analysis, naval projects, batteries, and control systems.