Mitsubishi Heavy Industries Technical Review Vol. 50 No. 3 (September 2013)
47Technologies to Improve Efficiency,Utilize Exhaust Heat of KU30GSI Gas Enginefor Distributed Generation System
HAJIME SUZUKI*1SHOUJI NAMEKAWA*2

MICHIYASU ISHIDA*3

HIROSHI YOSHIZUMI*4

ATSUSHI TAKAI*5

SHUHEI YAMANO*5

An increase in the number of power generation facilities with gas engines is expected withthe development of shale gas, as well as the utilization of gas pipe lines in addition to theexpanding need for the effective operation of power generation facilities such as the distributedgeneration system and smart grid. Mitsubishi Heavy Industries, Ltd. (MHI) covers a wide power
range of lean-burn gas engines, from the high-speed GSR model to the mid-speed KU30GSI model.
This report will mainly describe the efficiency improving technology of the KU30GSI-PLUS
engine, which has achieved a generation efficiency of 48.8%, placing it at the top level in the worldamong the engines in the same class. Technological development to utilize this energy in aco-generation system, as well as the application technology, will also be introduced.

|1. Introduction
Natural gas resources are attracting attention as a main fuel in the future against abackground of reducing environmental impact, as is shale gas development. In addition, therevolving momentum of electricity policies in many countries, and enhanced interest in distributed
power generation, which is effective against natural disasters, will increase the importance of theeffective utilization of energy (the so-called “smart energy network.”) Gas engines, which can use
various gas fuels including natural gas, have the features of good startability, load following
capability and flexible applicability of waste heat. They are also used in various applications
including Combined Heat and Power Plant (CHP), and are considered as an optimal selection toprovide an efficient energy solution in consideration of the social background noted above.
MHI has prepared a lineup of gas engines, a high-speed GSR model covering 305 to 1500
kW and a mid-speed KU30GSI model covering 3750 to 5750 kW, which are applicable tosmall-scale distributed power generation, co-generation in facilities or plants and dedicated utility
power generation. These gas engines enjoy a high reputation and expanding orders in themarketplace for their high performance and reliability.
This report will introduce the efficiency improvement technologies at MHI, in particular thelatest technologies of the KU30GSI-PLUS engine with its power generation efficiency of 48.8%, as
well as gas engine applications including waste heat utilization.

|2. Gas engine lineup
We started selling the KU30G and GSR model pre-chamber lean burn gas engines with sparkignition at the beginning of the 1990s. Since then, we have explored the improvement of efficiencyand output. In 2000, the micro pilot ignition system was adopted, and the high-efficiency and*1

Chief Staff Manager, Yokohama Engine Department, Engine Division, General Machinery & Special Vehicles*2

Deputy Director, Engine Engineering Department, Engine Division, General Machinery & Special Vehicles*3Manager, Yokohama Engine Department, Engine Division, General Machinery & Special Vehicles*4

Yokohama Engine Department, Engine Division, General Machinery & Special Vehicles*5

Chief Staff Manager, Engine Engineering Department, Engine Division, General Machinery & Special Vehicles

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 3 (September 2013)48

high-output KU30GA model gas engine entered the market, attaining a large domestic market
share. The latest four stroke-cycle KU30GSI and GSR engines are high-efficiency, lean-burnspark-ignition engines with pre-combustion chambers.
The KU30GSI gas engine has a high power generating efficiency, and with the increase of
the exhaust temperature, a high total efficiency is achieved, making it appropriate for applications
such as exhaust heat regeneration and Combined Heat and Power (CHP) generation. The KU30GSIengines, which have a maximum output of 5750kW, are also used in applications for the utility andindependent power generating businesses, in addition to CHP use. To meet these needs, a newmodel of the KU30GSI-PLUS engine, which has achieved the world’s top level of generation
efficiency at 48.8%, was added to the lineup. The KU30GSI engine shares many parts with other
KU series models including diesel engines, and has approximately 80% of its parts in common with
the KU30GA engine, which realized a high reliability through its extensive track record of morethan ten years.
The GSR gas engine is a high-speed gas engine that achieves high reliability and part supply
efficiency by utilizing common parts with the SR diesel engines, the same as the KU30GSIdevelopment method. The lineup of GSR gas engines includes engines with radiator coolingspecifications to cope with the increasing demand for Business Continuity Planning (BCP) after theGreat East Japan Earthquake, in addition to those with cooling tower specifications aiming for thehigh power generating efficiency ordinarily required in Japan. Both specifications have the functionof Black Out Start (BOS: Immediate starting in case of blackout), and applicable to the anti-disasterand security preservation operations. The “MEGANINJA® (Mitsubishi Energy Gas PackageNINJA Series)” containerized generator set has also been added to the lineup. The concept of theseries is “rapid transportation, rapid installation and rapid generation” through the adoption of a
portable radiator, compared to conventional generator sets which require the installation of theengine, generator and auxiliary equipment independently, in addition to the piping and wiringwork. A conventional generator set needs at least 30 days from installation to the start of electrictransmission. MEGANINJA can easily start power transmission and supply the demand in a shortperiod of time in areas without sufficient grid infrastructure, even overseas.
In these multiple engine applications combining KU30GSI and GSR engines, effective
power generation corresponding to demand is possible, and power generation plants that can start
supplying power in the absence of a power supply grid can be realized. Figure 1 shows the MHI
gas engine, and Table 1 shows the main specifications.

Figure 1

MHI Gas EngineMitsubishi Heavy Industries Technical Review Vol. 50 No. 3 (September 2013)49

Table 1Model
Number of cylinders
Bore/Stroke
Engine speed
Generator output*
Generation efficiency*
NOX (O2=0%)
Engine weight

Main specifications
GSR

GSR2
6 - 16

mm
min-1
kW%
ppm
t

170×180
170×220
1000-1800
1000-1500
305 - 1015
380 - 1500
41.0 - 43.4
< 320
2.2 - 8.1

KU30GSI-PLUS
12 - 18
300×380
720/7503650 - 5750
46.5
48.8
< 320
40 - 60

KU30GSI*Using a standard gas complying with ISO3046 and MHI recommendations|3. Power generation technology of high-efficiency gas engines
The utilization of the Miller cycle has been the general trend to improve efficiency in recentyears. Higher combustion and supercharging pressures are required for more effective utilization of
the Miller cycle. In other words, sufficient margin to knocking and the retention of a highsupercharging efficiency at high pressure ratio are technical problems.
In the KU30GSI-PLUS engine, the technical target was stable and rapid combustion toensure sufficient margin to knocking, and the design concept was the elimination of late flame
transfer and uneven fuel/air mixture in the combustion chamber. The City Gas 13A used in Japan
has a methane number of 65, which is lower than that of natural gas. Consideration to ensure theknocking margin is important to increase the efficiency.
To increase the Miller cycle effect, a greater amount of air corresponding to the effect isrequired. In addition, a high supercharging pressure, while retaining a high supercharging
efficiency, must be attained. The MHI MET-MB model turbocharger developed for highsupercharging pressure and efficiency was installed on the KU30GSI-PLUS engine to realize highpower generation efficiency.
Moreover, considering the reduction of unburnt gas in the exhaust, the thorough reduction ofdead volumes in the combustion chambers including the pre-combustion chamber and piston, theoptimization of pre-combustion chamber jet diameter and angle and the piston shape improvement
drastically reduced the Total Hydro Carbon (THC) emissions.

3.1

Sufficient margin to knocking and improvement of combustion stability

Generally, a high output and high efficiency gas engine with a pre-combustion chamber isoperated within a very narrow air fuel ratio squeezed between the knocking and misfiring region.
Therefore, the cycle to cycle fluctuation of mixture formation in both the main and pre-chamber
can lead to a larger combustion fluctuation. In many cases, such combustion fluctuation iscontrolled by an anti-knocking governor, etc. In the development of the KU30GSI-PLUS, wesought a technical solution by stabilizing the combustion while not relying on the avoidancecontrol.
We have optimized the combustion chamber shapes including that of the pre-chamber, andwere able to obtain combustion stability and high efficiency. Figure 2 shows a comparison ofCov-Pmax, which indicates combustion pressure fluctuation, before and after the improvement.
Cov-Pmax decreased significantly by approximately 40%, and stable operation with a higher
efficiency was realized, even when City Gas 13A was used as a fuel. The optimization reduced thefluctuation among cylinders, and resulted in a very uniform and stabilized combustion throughout
the entire engine.
As a result of the above, a sufficient knocking margin is ensured by reducing the fluctuations
among cylinders and stroke cycles, even under the higher combustion pressure conditions
associated with the strong Miller concept, thereby attaining higher power generation efficiency.

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 3 (September 2013)
50Figure 2

3.2

Cov-Pmax comparison before and after improvement

Reduction of dead volume

A reduction in dead volume is a common technique in the gas engine designing field. In
particular, the air fuel mixture propagated into the narrow space and clevis in the combustion
chamber and the unburned mixture in the later phase of combustion will not only result in
degradation, but will also trigger abnormal combustion such as knocking. Dead volume reduction
has been considered in the KU30GSI engine, such as eliminating the starting valve passage andreducing the clearance between the liner and cylinder head. In the case of the KU30GSI-PLUS
engine, we concentrated on further reduction of the dead volumes, such as the clevises around thepre-chamber and the topland of piston crown, and the clevises around the intake and exhaustvalves. (Figure 3) As a result, the total dead volume was reduced by 27%, and a 23% reduction of
unburned fuel emissions was achieved.

Figure 33.3

Dead volumeAdoption of turbocharger with high pressure ratio

The MHI MET42MB turbocharger, which is optimized for the Miller cycle and can sustainhigh turbocharger efficiency in a high pressure ratio zone, is employed for the KU30GSI-PLUS
engine. The MET42MB turbocharger has optimized its impeller and turbine peak efficiencies,
while maintaining reliability in the high-speed rotating range, and the sustainment of highturbocharger efficiency at a high pressure ratio is achieved. Turbocharger efficiency equivalent tothe MHI MET42MA, which was used on the conventional KU30GSI engine, is ensured in thehigher pressure ratio range of 4.0 to 4.5, and higher efficiency with a strong Miller cycle is realized.
Figure 4 shows a comparison of turbocharger efficiency.

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 3 (September 2013)
51

Figure 4 Turbocharger efficiency|4. Waste heat utilization technology of gas engines energy
We have developed gas engine technologies applicable to the improvement of the efficiencyof waste heat recovery, not only gas engines, but also auxiliary equipment, for the effective
utilization of energy.

4.1

Effective utilization of engine cooling water energy

In a gas co-generation system, total efficiency exceeding 80% is possible considering waste
heat recovery from steam, hot water and cooling water. In some cases, however, the recovered hot
water energy cannot be effectively used, such as in a self-generating plant for a factory, because therecovered temperature level of the hot water is too low. From the perspective of this kind of need,suggestions on how to enhance the utilization of hot water from the viewpoint of the effective
utilization of energy is one task for the future.
Technical development to utilize the energy of engine cooling water is under way aiming toexpand the effective utilization with the KU30GSI-PLUS engine. In this development, the coolingwater temperature at the engine outlet is raised to 110 - 115ºC, in order to generate steam under at
atmospheric pressure. Combustion testing was completed with a single-cylinder test engine, andverification testing using a multi-cylinder engine began from 2013. The combustion tests and theengine reliability study have already been completed, and durability testing of the engine andauxiliary equipment are now under way. We plan to finish the study at the end of 2013, and tolaunch the product.
If the aforementioned cooling water temperature can be achieved, and the flash steam at
atmospheric pressure is pressurized with a steam compressor by adding steam from the exhaust gas
boiler, an increase in energy of more than 10 %pt (pcp) is expected as the amount of steam
recovery, including the loss power required by the equipment. (Figure 5)

Figure 5

Effective use of engine cooling water energy

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 3 (September 2013)
52

4.2

Application examples of various waste heat recovery implementations

As mentioned above, efforts for the more effective use of high temperature cooling water
have progressed. In addition, there are some application examples where cooling water at existing
temperature levels has been effectively used.
Figure 6 shows an example of a gas engine plant, where an 18KU30GSI engine using
natural gas fuel has been installed and chilled water of 5.6°C is generated with a multi-energy
absorption chiller. This plant was constructed at a university in the United States, and has been inoperation since 2012. The generator end electricity of 5500kW, and chilled water corresponding toapproximately 3500kW supplied from this plant, greatly contribute to the energy savings of theuniversity, especially during the summer.

Figure 6 Example of exhaust heat use (KU30GSI)

An example of the combination of the exhaust heat recovery application and BCP mentioned
above is shown in figure 7. This plant has a GS16R engine generator installed, as well as a gas
supply facility of Liquefied Propane Gas (LPG), in preparation for a disruption in the daily supplyof city gas supply in a disaster. This plant also features a system to utilize waste heat. The waste
heat is used in various ways as steam utilization from an exhaust gas boiler, as air conditioning
with an absorption chiller and as a room heater and hot water supply using high temperature
cooling water through a heat exchanger.

Figure 7

Example of exhaust heat recovery (GS16R)

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 3 (September 2013)
53

These are just some examples, and MHI gas engines have been developed not only for highpower generation efficiency, but also for flexible application in order to realize high total heatefficiency.

|5. Conclusion
Our company has prepared a lineup consisting of the high-speed GSR and mid-speed
K30GSI gas engines, and is able to meet the demand of a wide range of flexible applications. The
latest KU30GSI-PLUS engine has a high load-following capability such as a starting time of 7
minutes or less, as well as favorable environmental performance. The engine realizes a good power
generation efficiency of 48.8%, even using the City Gas 13A (methane number 65) fuel unique toJapan. The engine will contribute to the cost reduction of power generation while LNG is attracting
global attention as a fuel in the future, and will also help to facilitate the reduction of environmentalload and the effective use of energy resources.
From the start of development work, MHI gas engines have been developed to meet theneeds of society and our customers. We will continue the development of useful technologies, andprovide various solutions.

References
1. Ishida. et al., CIMAC Congress 2010, Bergen ; Paper No.109
2. Suzuki. et al., CIMAC Congress 2013, Shanghai ; Paper No.421
3. Development of 1.5MW High Efficiency Gas Engine and Container Type Generation Set, Mitsubishi
Heavy Industries Technical Review Vol.50 No.1(2013) pp.7-9
4. Osaki. et al., An Environmentally Friendly and Highly Efficient Combined Heat and Power Plant with a
MACH II-SI (KU30GSI) Gas Engine for the University of Central Florida in the United States,
Mitsubishi Heavy Industries Technical Review Vol.48 No.1(2011) pp.11-16