The Development of 1 MW
Class Gas Engine an d I t s
Application to Cogeneration
Systems
TAKASHI KADO*1

KOJI HORIMOTO*1

YOSHIHIKO OSAKA*1

MASAKI OGAWA*1

TOMOHIRO NOGUCHI*1

HIROKAZU NARITA*2

Since the end of the 20 th century, gas engines fueled by natural gas, known as “clean energy,” have attracted attention as
outstanding power generation systems in addressing global environmental issues. They are increasingly in demand because theyemit less carbon dioxide (CO2 ), which causes global warming, sulfur oxides (SOx), which are responsible for acid rain, and nitrogenoxides (NOx), which lead to environmental problems. With this background, Mitsubishi Heavy Industries, Ltd.(MHI) has developed
a commercial highly efﬁcient 1 MW class (280–1000 kW) gas engine, which is friendly to the global environment.

world’s highest generating efﬁciency of 41.5% (380 kW) wasmarketed. Furthermore, a 1000 kW Miller cycle gas engine
with a generating efficiency of 41.7% will be introduced in
the near future. Figure 1 shows the history of the efﬁciency
improvements. While this figure shows products for the60 -Hz region, the following development efforts were also
made for the 50-Hz region:• GSR Miller: Generating efﬁciency 39% (320, 635, and 845kW), 2002
• GSR Miller: Generating efﬁciency 40% (635 and 845 kW),2006
• High-powered GSR Miller: Generating efﬁciency 40% (700and 930 kW), 2006

1. Efﬁciency improvement of gas engines
1.1 Features of gas engines
T he main f uels for gas engines are natural gas andcity gas (13A). They generate less carbon dioxide (CO 2 ),which causes global warming, because the main component
methane (CH 4 ) contains four times more hydrogen atoms(H) than carbon atoms (C), which is over twice the ratio of
petroleum fuels. Hydrogen becomes water when combusted.
They also do not emit sulfur oxides (SOx), which cause
acid rain, because the fuel does not contain sulfur atoms.
Moreover, natural gas and city gas contain no particulatematter (PM) and emit fewer nitrogen oxides (NOx), both ofwhich are detrimental to human health.
1.2 History of efﬁciency improvements in MHI’s gas
engines
In 1993, MHI introduced a gas engine that adopted anultra-lean-burn system whose generating ef f iciency atthat time was 34.3 –35.5% . Subsequently, in 2000, MHI
marketed a gas engine (GSR Miller) that adopted the Miller
cycle for a precombustion chamber-type lean-burn engine
developed jointly with Osaka Gas. The Miller cycle gas
engine had the world’s highest generating efficiency of40% for that class (280, 560, and 740 kW) at that time. In
2002, the company developed the Advanced Miller cycle
gas engine (GSR Advanced Miller; 305, 610, and 815 kW )by improving the efﬁciency and increasing the output of theMiller cycle gas engine, attaining what was then the world’s highest generating efficiency of 40.4% (305 kW) to 40.8%(610 and 815 kW ). With subsequent improvements, MHI
has attained a generation efﬁciency of 41.4% at 815 kW. Joint
development efforts with Osaka Gas continued, and in 2005,
a middle-sized GS6R 2 Miller cycle gas engine with theLaunch of the GSR2 Miller
Launch of the Advanced
GSR Miller

Generating efficiency (%)

45

Launch ofthe GSR Miller

The GSR2 Miller cycle

40

Advanced Miller cycle
Miller cycle

351995

Lean-burn2000

2005

2010

YearFig. 1 History of MHI’s improvement of gas engine efﬁciency

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 1 (Mar. 2008)*1 General Machinery & Special Vehicle Headquarters*2 MHI Sagami Hi-tech LTD.

29

2. Gas engine cogeneration system

Conceptual diagram of the Miller cycle

Cogeneration is a system that uses energy effectively
by generating multiple types of energy, such as electricity,
hot water, and steam, from a single energy source suchas nat ura l gas. Due to t he higher- energ y ef f icienc yand resultant reduction in greenhouse gas emissions as
represented by CO2 , this system is expected to bring about
positive economic effects such as energy cost reductions.
2.1 System conﬁguration
The component devices of the cogeneration system include
engines, generators, pumps, heat exchangers, silencers,boilers, and gas compressors, combinations of which canfurther expand the available selection. Therefore, marketing
required standardizing the basic system to readily satisfy
customer specifications. Cogeneration systems with a gas
engine as their core can be divided into hot water recovery
systems and hot water and steam recovery systems. The
difference between these two types is whether the heat fromthe engine exhaust gas is recovered in the form of hot wateror steam. To facilitate the production of the two types, thecomponents common to both, such as the engine, generator,
starting battery, lubricating oil tank, control panel, gasvalve equipment, and gas compressor, were integrated into
one package as the power generation unit. Simultaneously,
the components that could not be used in common wereThe Miller cycle

Occurrence ofknocking

VolumeInternal cylinder pressure

Internal cylinder pressure

Conventional cycle

Increase inwork units

VolumeCompression

Compression

Expansion

Expansion

Fig. 2 Conceptual diagram of the Miller cycle
This technology prevents knocking by decreasing the compression
ratio and improves the cycle efﬁciency by increasing the expansion
ratio.

• GS6R 2 Miller cycle gas engine: Generating efficiency
41.6% (315 kW), 2007
The GSR Miller, Advanced GSR Miller, and High-powered
GSR Miller together have a deliver y record of over 220
units across the country, earning a high reputation amongcustomers.

Waste heat recovery steam boiler

Steam outlet
Silencer

Exhaust gas
Feed water inlet

Exhaust air port
Hot water outlet
Jacket water heat exchanger
Hot water inlet
Gas engine

Precombustion
chamber
Main combustion
chamber

Cooling water outlet
Load balancing heat exchanger

Cooling water inlet
Intercooler heat exchanger

Generator

Intake air port

Battery

Air/fuel ratio
control

Automatic lubricating system

Generator control panel

Lubricating
oil tank

Auxiliary machinery

Gas compressor

Fuel gas

Solenoid valve

Fig. 3 Block diagram of the hot water and steam recovery system

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 1 (Mar. 2008)30

in the form of hot water by using a heat exchanger (totalefﬁciency 73.2–76.4%). The hot water recovery temperature
is set to a normal temperature range (83°–88°C, i.e., thetemperature range required for an absorption chiller and for
a Gen-link). Figure 4 shows an example of the hot waterand steam recovery scheme of the GS16R Advanced Miller
cycle system (815 kW).
2.3 Hot water recovery system
Figure 5 shows a block diagram of the hot water recovery
system. In this system, which has a total efﬁciency of 73.5 to77.6%, hot water is recovered through the following two lines.
• Heat from the engine exhaust gas is recovered in the formof hot water by the waste heat recovery water heater above
the auxiliary machinery.
• Heat from the engine cooling water and the hot water fromthe exhaust gas are recovered in the form of hot water by
the jacket water heat exchanger.
The temperature value of the hot water recovery systemis the same as that of the hot water and steam recovery
system. Optionally, this system can be used at higher recovery
temperatures (83°–90°C). Figure 6 shows an example of the
hot water recovery scheme of the GS6R Advanced Miller cycle
system (305 kW).
2.4 Examples of other applications
When exhaust gas is led directly into an absorption chiller
for heat recovery, heat radiation devices are installed above

Fig. 4 The Advanced Miller GS16R-815kW hot water and steam
recovery system in operation

integrated as auxiliar y machiner y incorporating heatrecovery devices to meet the two speciﬁcations separately.
In designing the package, a compact layout was realized,
while ma int a inabilit y was considered. Fur ther more,by adopting this cogeneration package conf iguration,site installation requires simply combining these units,
shortening the work period for site construction.
2.2 Hot water and steam recovery system
Figure 3 shows a block diagram of the hot water andsteam recovery system. A waste heat recovery steam boiler
is located above the auxiliar y machiner y. This system
recovers the heat from the engine exhaust gas in the form ofsteam and recovers the heat from the engine cooling water

Exhaust gas
Waste heat recovery water heater
Silencer
Hot water outlet
Exhaust air port
Jacket water heat exchanger
Intake air port

Hot water inlet
Gas engine
Cooling water outlet

Generator

Pre-combustion
chamber
Main combustion
chamber

Load balancing heat exchanger

Cooling water inlet
Intercooler heat exchanger

Battery

Generator control panel

Air/fuel ratiocontrol

Automatic lubricating system
Lubricating
oil tank

Gas compressor
Auxiliary machinery

To the distribution panelof the power receiving
and transforming room
Fuel gas

Solenoid valve

Fig. 5 Block diagram of the hot water recovery system

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 1 (Mar. 2008)

Automatic lubricating system31the existing range based on an accurate understanding ofcustomer needs. In addition, MHI intends to develop thehigh-efﬁciency technology that the company has cultivatedover the years further and to continue introducing productsthat can help prevent global warming.
References
1. Fukuzawa, Y. et al., Development of High Efﬁciency Miller Cycle
Gas Engine, Mitsubishi Heavy Industries Technical Review Vol.38
No.4 (2001)
2. Tsunoda, A. et al., MIT SUBISHI Lean-burn Gas Engine withWorld's Highest Thermal Efﬁciency, Mitsubishi Heavy Industries
Technical Review Vol.40 No.4 (2003)
3. Shimoda, H. et al., High Efficiency Miller Cycle Gas Engine
Generator with Clean and Low CO 2 Emission, Mitsubishi JukoGiho Vol.41 No.1 (2004)
4. Noguchi, T. et al., T he Further Progressed Gas Engine Co generation System with World's Highest Efficiency of 41.5% ,Mitsubishi Heavy Industries Technical Review Vol.42 No.3 (2005)

Fig. 6 The Advanced Miller GS6R-305kW hot water recovery
system in operation

the auxiliary machinery so that the system can introduce
exhaust gas through the gas duct directly. Several of theseunits have already been delivered to customers.

3. ConclusionsThe GSR Miller cycle gas engine cogeneration package
has attracted attention by attaining a generating efficiencyof 40% for the first time in this class. It has contributed toshortened delivery time and cost reductions, which wererealized by using the standardized package for each engine
model, as described above. As a result of these efforts, thenumber of orders has increased steadily. As the need forcogeneration is expected to rise in the future due to risingenergy prices and increasing demands for CO 2 emissions
reduction, MHI is considering expanding production beyond

Takashi Kado

Koji Horimoto

Yoshihiko Osaka

Masaki Ogawa

Tomohiro Noguchi

Hirokazu Narita

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 1 (Mar. 2008)32