MHI has tweaked its MACH-30G gas engine and produced the Mach-II SI, claimed to be, in heat recovery mode, one of the most efficient gas engines available in its class.

Mitsubishi Heavy Industries has developed and begun operational verification testing of its MACH II-SI, a new gas engine with, says MHI, enhanced energy efficiency and reliability. The MACH II-SI was developed from the MACH-30G, many units of which have been sold in Japan, but whereas its ancestor uses a micro-pilot ignition system, the new engine adopts a spark ignition (SI) system that eliminates the need for an auxiliary liquid pilot fuel such as light oil.

In developing MACH II-SI, MHI focused on further enhancement of the thermal efficiency. As a result, the new engine has achieved an efficiency performance – in combined power and heat mode (heat energy recovery via steam) – of 66.1%, the world’s highest rating among 6 MW class engines, and representing a generation efficiency improvement of 1 percentage point. This figure was achieved under the terms of ISO 3046 using gas with a methane number of 80, the standard quality of gas MHI recommends. MHI expects the MACH II-SI series, of which the power output ranges from 3650 kW to 5750 kW, to significantly contribute to increasing demands for carbon dioxide emissions reduction.

Efficiency increase

The development process was centred on enhanced heat recovery in steam generation and effective utilisation of exhaust gas energy. The company also has shortened full-load lead-time after engine start by 50%, which contributes to an enhanced load-following capability. In order to boost power generation efficiency, MHI redesigned the combustion chamber, including the cylinder cover and piston. By optimising formulation of the fuel-air mixture, as well as improving the pre-chamber’s shape and fuel-air mixture ratio, the company has raised combustion efficiency and reduced thermal loss.

In developing the technology used to achieve these improvements, MHI applied results gained from a joint development project (‘Development of technology for ultra high-efficiency natural gas engine combined systems’) under way since 2005 with the New Energy and Industrial Technology Development Organisation (NEDO) and the Japan Gas Association. It is intended that the technologies employed in the new engine to enhance power generation efficiency will also be applied to existing MACH engines with the micro-pilot ignition system.


MHI conducted testing of the first MACH II-SI engine – to confirm start-up performance, engine performance and control system – last summer at the company’s Yokohama Machinery Works. As all targeted goals were achieved, the new engine has now progressed to the next stage of testing, including durability testing, towards final verification of its enhanced reliability.

The parent technology

Since its introduction in 2001, MHI has delivered more than 150 units of the MACH gas engine, which were themselves developed from the KU30 diesel, and some of the KU30 units have already operated more than 170 thousand hours. In addition to new technical developments, the expertise accumulated through this operational experience have been incorporated into the MACH II-SI to promote high reliability.

MHI has also established a Customer Service Centre at the Yokohama works to provide 24-7 remote support service on a contract basis for operational support of user plants as well as emergency services, and started up new service centres in Hiroshima and Nagoya.