Power and Energy System Research & Development Group

This group aims to develop an environment-friendly marine engine system by using SCR (Selective Catalytic Reduction), which uses a catalyst to reduce NOx emissions in the exhaust gas of marine diesel engines. This group is promoting research and development, such as high functionality, durability improvement, and miniaturization of SCR. In addition, to prevent global warming and save energy, this group is conducting R & D on hybrid power systems and exhaust heat recovery technology using Stirling engines. Furthermore, this group is conducting R & D on combustion improvement technology by improving the fuel injection system (electronically controlled fuel injection, hybrid injection system (HIS), etc.).

1. NOx Reduction Technology

This group has engaged in research and development of marine SCR technology. SCR (Selective Catalytic Reduction) technology is an exhaust gas aftertreatment technology that reduces NOx in exhaust gas. We can reduce NOx using a catalyst and a reducing agent (ammonia gas or urea water). NOx reacts with ammonia (NH3) on the catalyst, as shown in the below figure, and it is decomposed into nitrogen and water (see the figure below).
 So far, we have conducted a performance evaluation test using a 4-stroke marine diesel engine equipped with an SCR and have developed an SCR system for field tests. In addition, we identified many technical issues through long-term actual ship tests.

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2. Marine Hybrid System

Traditionally, ships have been powered by high-efficiency diesel engines with thermal efficiencies of more than 50%. On the other hand, the thermal efficiency of gasoline engines in cars is about 35%, and the thermal efficiency of jet engines in aircraft is about 30%. The power source of a ship is exceedingly effective in using energy, as compared with other power systems. However, due to social issues such as the recent environmental problems represented by global warming and the fluctuation of oil prices, further reduction of fuel consumption is required in the shipping field. Against this background, to reduce global warming gas emitted from ships, next-generation hybrid systems for ships that make the most of the features of high-efficiency diesel engines and use electric and natural energy are drawing attention.
 Because the operation of the automobile hybrid system is a frequent repetition of starting and stopping, we can save energy by using the energy recovered at stopping (regenerative energy) at the start-up time. In addition, we can use the engine and the electric motor together when high torque is required, such as when starting the vehicle, to save fuel by reducing the maximum engine output. On the other hand, ships operate at a constant speed most of the time, so we cannot expect regenerative energy use like automobiles. In addition, since ships operate near the maximum engine output (about 80% of the maximum output), it is not appropriate to reduce the engine output. For these reasons, this group is studying a system that makes the best use of the characteristics of high-efficiency diesel engines by making effective use of electrical energy.

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3. Hybrid Injection System (HIS)

Reducing air pollutants emitted from ships is a serious issue. This group has engaged in the research and development of combustion technology that can handle a variety of fuels for marine diesel engines. As a result, we developed a hybrid injection system (HIS) that combines a conventional mechanical fuel injection device with a small electronically controlled fuel injection device (using a common rail for automobiles) to cope with poorly ignitable fuel. By performing injection (assist injection) with a small electronically controlled fuel injection device at appropriate timing, we confirmed effects such as improvement of ignitability, reduction of smoke generation, and reduction of NOx generation.

The features of this hybrid injection system are as follows.

• We can retrofit a simple and inexpensive device to an existing engine and perform restoration with ease.
• The original mechanical fuel injection guarantees safety and redundancy, which is crucial for ships. Assist injection is for improving performance and does not deteriorate it.

In addition, the effects and possibilities of the hybrid injection system are as follows.

• It improves combustion of poorly ignitable fuels and allows the use of various fuels.
• It improves combustion in a low load range where combustion conditions are severe.
• There is a possibility of improving fuel efficiency equivalent to a fully electronically controlled fuel injection device. We plan to collect detailed data and investigate it in the future.
• NOx can be reduced by using after injection. We plan to investigate it in more detail.

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4. Stirling Engine for Waste Heat Utilization

The Stirling engine is an external combustion engine that obtains drive power by expanding and contracting the gases inside by heat sources of different temperatures. Its theoretical thermal efficiency is high. Since it is an external combustion engine, it can use any high-temperature heat source.
 This group has been conducting R & D on Stirling engines that utilize the exhaust heat in exhaust gas emitted from marine diesel engines. Based on the results obtained, we developed a heat recovery system using a Stirling engine and installed it aboard the electric propulsion ship "Tsuruyomaru" in October 2011. This Stirling engine can generate about 3kW of electricity from exhaust gas at about 300 degrees Celsius as the heat source. A control system for starting and stopping power generation has also been developed at the same time so that heat recovery power is generated whenever the ship is in operation.

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5. Marine Gas Engine

Today, most marine engines are diesel engines. Diesel engines are at a high technological level in terms of reliability, fuel efficiency, durability, load response, etc. On the other hand, the large amount of emissions of environmentally hazardous substances such as NOx, SOx, and soot has become an issue.
 In recent years, there has been an increasing international sentiment toward reducing such hazardous substances emitted from ships and research and development of environmental load reduction technology for vessels has been promoted in various fields. Under these circumstances, marine gas engines that can significantly reduce the emission of environmentally hazardous substances are drawing attention. A gas engine is an engine that uses natural gas as fuel and has the environmentally friendly features that the fuel is clean and does not simply generate environmentally hazardous substances when burned. This group is promoting research on the use of gas engines in ships. Using a gas engine with a power generation output of 400kW, we are conducting research on the effects of differences in fuel gas components on engine performance, systems that detect abnormal combustion, exhaust gas recirculation, and hydrogen-mixed combustion.