Mitsubishi Heavy Industries Technical Review Vol. 56 No. 2 (July 2019)
1Development of High-efficiency
2MW High-speed Gas Engine(Completes 9,000+ Hour Validation)

M i ts u b i s h i H e a v y I n d u s t r i e s E n g i n e& Tu r b o c h a r g e r, L td .

In the segment of distributed power sources, power generation by means of a gas engine
holds an important position since gas engines emit less CO2 from burning natural gas than coaland heavy oil, i.e., its exhaust emissions are cleaner and its thermal efficiency is fairly high.
Nevertheless, the key that attracts customers and motivates them to purchase one is how
economical the unit price of a gas engine power generation is, compared with the unit price ofpower from the grid. Namely, the product merchantability is dependent on the realization ofappealingly high generation efficiency. It is also key to design the engine with the smallest
dimensions possible, especially for installation at sites in urban areas.
To meet these needs, Mitsubishi Heavy Industries Engine & Turbocharger, Ltd. has beendeveloping the new 2MW-class G16NB gas engine, which features the world's most advanced
combustion control and turbocharging technologies (Figure 1). An overview of the G16NB engine
is described below.

Figure 1

G16NB gas engine|1. Features
1.1

Pre-chamber initiated lean-burn combustion

The G16NB engine adopts lean-burn technology to achieve both higher thermal efficiency
and lower NOx emissions. The difficulty of ensuring constant and stable ignition per cylinder, atypical problem for lean-burn engines, has been solved for the G16NB engine by means of the
pre-chamber torch jet ignition system.

1.2

Miller cycle

In case where the premixed combustion is selected, abnormal combustion (engine knocking)often occurs because the higher compression ratio causes increase in both temperature and pressure
in cylinders. To avoid this known problem, G16NB engine has employed Miller cycle that canincrease the expansion ratio without increasing the compression ratio to control the elevation of
in-cylinder temperature and thereby avoid engine knocking. To this end, early intake valve closing
strategy has been applied.

1.3

Two-stage turbocharging system
G16NB engine uses two-stage turbocharging system to achieve higher output and efficiency.

Mitsubishi Heavy Industries Technical Review Vol. 56 No. 2 (July 2019)
2The air compressed by the lower-stage turbocharger is cooled by the intercooler and transferred tothe higher-pressure turbocharger so as to enhance the overall turbocharging system efficiency. Thisultimately contributes to reducing the pumping loss and increasing thermal efficiency.

1.4

Wastegate valve

Whereas gas engines in general use an intake throttle valve to control the air-fuel ratio, theG16NB engine controls the air-fuel ratio by changing the turbocharger speed via a wastegate valve.
This control can eliminate the risk of pressure loss by the throttle valve, resulting in even higher
thermal efficiency.

1.5

Ignition timing control

While ignition timing advancement is effective in increasing the degree of constant volume
and thermal efficiency, it cannot avoid engine knocking. By detecting engine knocking during
operation and giving feedback control to ignition timing, continuous operation with high thermalefficiency has been ensured for the G16NB engine. The engine adjusts the ignition timing
according to the vibration readings from the acceleration sensor provided for each cylinder,
computes the knocking intensity using MHIET’s proprietary logic and uses it to control the ignition
timing for each cylinder.

|2. Main specifications
The main specifications of the G16NB engine and the GS16R2 engine currently on themarket are shown in Table 1. Although the engines have exactly the same displacement, theG16NB engine has achieved higher output and generation efficiency, which indicates that theG16NB engine has the greater advantage and value as a distributed power source. The generating
efficiency of the G16NB engine is 44.7%, which is one of the world’s highest among 2MW-classhigh-speed gas engines.
Table 1 Main specifications of the new G16NB* gas engine and the existing GS16R2 gas engine
Engine model
G16NB
GS16R2Engine output
kWe
2000
1000
Engine speed
min-1
1500
1000
Generation efficiency based on lower heating value%
44.742.3
Cylinder bore x strokemm
170×220
Cylinder layout/Number of cylinders－V type/16 cylinders
Displacement
L80
Turbocharger－Two-stage turbocharging
Single-stage turbocharging* Values represent current performance and specification, subject to change before placing on the market.

|3. Future action
The G16NB engine has been operating in a co-generation package supplying electricity andheat to be used in MHIET’s own Sagamihara factory (Figure 2). Using this demonstration
package, the engine is being evaluated for reliability over the long term under actual operating
conditions and improvements are made as appropriate. The combined service hours of thedevelopment G16NB engine and this demonstration G16NB engine exceed 9,000 hours, and thesoundness of the major components has been verified in inspections. Feedback from the evaluationand validation will be implemented in the production G16NB engine to be marketed as a gas
engine cogeneration system.

Figure 22MW gas engine power generation package