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YANMAR Technical Review


Development of Class-leading High-Efficiency Gas Engine Co-Generation System


The EP800G is a high-efficiency co-generation system with low environmental impact, featuring power generation efficiency of 41.2% and NOx emissions of less than 200 ppm.

The EP800G is designed with consideration for transportation and installation, with a per-kW installation footprint 19% smaller than the current model. It has an open skid design that can be separated into three pieces for on-site transportation, making it suitable for installation in buildings.

In developing the control system for the EP800G, Yanmar targeted standardization and flexibility, providing the following features.

(1)Robust operation (system does not shut down easily in the event of major failure)

(2)Lower costs (including installation costs)

1. Introduction

Increasing use is being made of gas engine co-generation systems fuelled with natural gas because of their energy efficiency, low CO2 emissions, and superior economics, with installation in recent years being further boosted by rising demand for the systems as emergency generators to improve power supply security in the event of natural disasters, etc. The 2014 Basic energy plan by the government indicates an intention to facilitate the sale of power generated through co-generation and to proceed with support measures to encourage its installation(1). This article describes the 800 kW (60 Hz) EP800G high-efficiency gas engine co-generation system that Yanmar developed in response to these market requirements.

2. Development Background

Yanmar Energy System Co., Ltd. has a high share of the market for gas engine co-generation systems in the 100 to 1,000 kW range (approximately 60% in 2013, based on number of units sold), with an existing product range made up of its EP370G and EP700G mid-range (300 kW+) gas co-generation systems for 50 Hz regions, and the EP400G for 60 Hz regions (2), as listed in Table 1. Yanmar set about the development of the EP800G to expand its 60 Hz product range and satisfy the requirements of business continuity planning. In terms of performance, Yanmar targeted high power generation efficiency to make maximum use of natural gas while also helping reduce the impact on the environment. Anticipating growing demand in the future for the replacement of existing plants and installation in existing buildings, Yanmar also developed the system to be capable of being transported along the narrow access ways available in such situations. To improve power supply security by reducing the frequency of system shutdowns, Yanmar also sought to provide the system with robust operation to ensure it does not shutdown easily.

Table 1 Mid-range Gas Engine Co-generation Systems (as of April 2015)

3. Co-generation Systems

Fig. 1 shows an overview of a co-generation system compared to a conventional power generation system. A co-generation system supplies both heat and power, generating electric power by using an engine, a turbine, a fuel cell, or other technique fueled by natural gas, fuel oil, or LP gas, and also recovering the associated waste heat(3). Locating co-generation close to demand enables effective use to be made both of the electric power and waste heat, with the result that around 70 to 80% of the energy contained in the fuel is put to use (overall efficiency). This energy efficiency provides both superior economics and reduced CO2 emissions. Systems can also be used as backup generators to supply power during outages on the commercial grid, thereby ensuring a reliable supply of electric power and heat during emergencies.

Fig. 1 Overview of Co-generation System and Conventional Power Generation System
(from Yanmar Website)

The EP800G co-generation system is driven by a gas engine. The following sections provide an overview and describe its features.

4. Development Project (Product Features)

4.1. External Appearance and Specifications of EP800G

Fig. 2 shows a photograph of an EP800G, Fig. 3 shows its internal layout, and Table 2 lists its specifications. The EP800G generates electric power by using its gas engine to drive a generator. It achieves high overall efficiency by recovering the thermal energy from the exhaust gas and engine cooling water. The system consists of the gas engine, generator, cooling water and other pumps, heater, ventilation fans, and control panels and they are arranged in a single package.

Fig. 2 EP800G (Steam Boiler Model)
Fig. 3 Internal Layout of EP800G Generator Unit
Table 2 EP800G Specifications

4.2. High Efficiency and Low Impact on Environment

The EP800G uses the AYG40L-SE V12 engine, which is based on the widely used and highly reliable AYG20L-SE straight six engine from the Large Power Products Operation Business of Yanmar. EP800G development achieved power generation efficiency of 41.2%, class-leading performance for a Miller cycle gas engine, through the use of a highly efficient turbocharger and optimization of sub-combustion chamber lean burn together with the adoption of technologies such as individual cylinder control for fuel gas injection and Miller cycle operation, as shown in Fig. 4. The EP800G also achieved the load input ratio to 40% through optimization of lean burn combustion.

In terms of environmental performance, while many engines in this class require a NOx reduction system to comply with emission standards, the EP800G can satisfy the urban-use standard of less than or equal to 200 ppm NOx (at O2 = 0%) without use of a NOx reduction system.

In this way, the EP800G satisfies the conflicting performance objectives of high efficiency and lower environmental impact.

Fig. 4 Power Generation Efficiencies for Co-Generation(4)
(* Based on material from New Energy and Industrial Technology Development Organization (NEDO) website)

4.3. Smaller Installation Footprint and Easier Transportation for Installation

If co-generation is to be installed in urban areas, it needs to have a small footprint (required floor space). Fig. 5 shows drawings of the package and open skid models of the EP800G and Table 3 lists a comparison of installation footprints. Whereas the EP400G requires an area of 22.0 m2 to install two generator units (same for both package and open skid models), the EP800G generator unit has been designed to be more compact, taking up only 17.9 m2 (for the package model) or 13.1 m2 (for the open skid model), corresponding to a reduction of 19% and 41% respectively in per-kW footprint.

Fig. 5 Drawings of Package Model (Left) and Open Skid Model (Right)
Table 3 Comparison of Installation Footprints (Relative to EP400G)

Furthermore, it is not uncommon for access to installation sites in existing buildings to be difficult, meaning that systems need to be transported to the site in separated form. This makes it very important for the system to be easy to separate in order to keep installation costs down. As shown in Fig. 6, for ease of on-site transportation, the EP800G is available in a version that allows the generator unit to be separated into three parts, the longest of which is 4 m.

Fig. 6 Generator Unit Design that can be Separated into Three Parts (Open Skid Model)

4.4. Higher functionality of Control System

Yanmar develops its own control systems to make them more reliable and to facilitate engineering application. The practice in the past was to outsource control system development to the control panel supplier, and Yanmar established a highly reliable control system by standardizing the specifications on the earlier EP350G model. The disadvantage of standardizing specifications, however, is that it makes it more difficult to satisfy customer-specific requirements and becomes an obstacle to increasing commercial value. By developing its own control systems, Yanmar has been able to combine both standardization (for reliability) and flexibility (for easier response to on-site engineering requirements).

Fig. 7 Basic Concept of EP800G Control System
(1)Avoidance of major failure shutdown by reducing output

With higher generation output comes an increased risk of incurring penalties due to exceeding the contracted level of power use when an unexpected system shutdown occurs. On the EP800G, Yanmar has reviewed past shutdown items by major failures and adopted a control system that does not shut down the system immediately but allows to continue its operation within the output range that does not affect the engine when a major failure occurs. Fig. 8 shows the results of testing in which this control system was simulated. An example case is when high outdoor air temperatures during the summer cause a short-term rise in the temperature of system components. Whereas this would have caused the system to shut down by a major failure in the past, the new control system avoids shutting down in certain cases and instead avoids any effect on the engine by temporarily reducing output and then gradually increasing it again once the temperature has fallen. This should reduce the frequency of unexpected system shutdowns.

Fig. 8 Image of Output Control to Avoid Major Failure Shutdown
(2)Improvements to on-site engineering application

Fig. 9 shows a diagram of the power receiving system and power generation system at a customer site. As there are varieties of the power receiving system, it is difficult to apply using only the standard system. Accordingly, the engineering staff at the branch office worked with the customer to design an individual interface panel to absorb the incompatibilities between the power generation system and the customer’s power receiving system. It was also necessary to handle the customer’s request for additional equipment to be installed. Because the control system was developed in-house, some of the auxiliary equipment functions handled by the engineering team at the branch office were able to be adopted as standard functions and incorporated into the generator control panel. This succeeded in reducing the total cost, including installation work, by reducing the need for customized design, simplifying and reducing the wiring requirements, and enabling site-specific equipment functions to be incorporated into the EP800G control panel.

Fig. 9 Power receiving System and Power Generation System
(3)Support for field servicing

For field servicing, Yanmar has developed a software tool that customer support staff can use to monitor and record system measurements on-site. Fig. 10 shows an example screen. This improves customer support by enabling failure diagnosis and control operation checks to be performed on-site.

Fig. 10 Example Screen of On-site Tool for PCs

5. Conclusions

This article has described how the EP800G co-generation system creates customer value (life cycle value: LCV) through features that include energy efficiency, lower CO2 emissions, and greater security of electric power supply. Yanmar believes that wider adoption of co-generation systems like this will help achieve its mission statement objective of enriching people’s lives for all our tomorrows by overcoming the challenges our customers face.


  • (1)Basic Energy Plan, April 11, 2014
  • (2)Nippon Engine Generator Association
    FY2013 database of on-site generation system installations
  • (3)Documents of Combined Heat and Power Promotion Office, Agency for Natural Resources and Energy
  • (4)Website of the New Energy and Industrial Technology Development Organization (NEDO)
    (as of 04/28/2015)


The original technical report is written in Japanese.

This document was translated by R&D Management Division.


Development Division

Yusuke Oda