Mitsubishi Heavy Industries Technical Review Vol. 50 No. 1 (March 2013)
49

Development ofEPA Interim Tier 4 Certified Small Diesel Engine
KENJI HIRAOKA*1

SATOSHI YAMADA*1

KAZUNARI IDE*2

KAZUKI NISHIZAWA*3

TOMOHIDE YAMADA*4AKIHIDE OKAJIMA*5Diesel engines are used as a power source for various industrial machines because they havegreater fuel versatility and are more fuel efficient than other internal combustion engines.
Meanwhile, emission regulations have been tightened year after year. In the United States, the EPA
Interim Tier 4 emission regulations for engines with a rated output of 56 kW or more to less than
75 kW become effective in 2012. To meet these regulations, a further reduction of emissions isrequired. The particulate matter (PM) emission amount, for example, needs to be reduced to 1/20
compared with the required level of the conventional regulations. MHI has developed the D04EG
engine in compliance with the EPA Interim Tier 4 emission regulations, which reduce the regulated
substances further than engines certified the conventional regulations, while also attaining higher
fuel efficiency.

|1. Introduction
Diesel engines are used as a power source for various industrial machines such as
construction and agricultural machinery because they have great fuel versatility and are fuelefficient. In the past, MHI developed and commercialized engines in compliance with the Tier 3
emission regulations to offer customers high-performance and high-reliability engines.
Meanwhile, emission regulations enforced mainly in Japan, Europe, and the United States
have been tightened year after year. Figure 1 shows the trend of emission regulations for off-roadengines established by the U.S. EPA.

Figure 1 U.S. EPA emission
regulations for off-road engines(56 to 75 kW)
The horizontal axis represents NOx+HC for
Tier 3, and NOx for Tier 4 and later.

For engines with a rated output of 56 kW or more to less than 75 kW, the EPA Interim Tier 4emission regulations that become effective in 2012 in the United States require the further
reduction of emissions. The PM emission amount, for example, needs to be reduced to 1/20
*1Yokohama Resarch & Development Center, Technology & Innovation Headquarters*2

Manager, Nagasaki Research & Development Center, Technology & Innovation Headquarters*3

Chief Staff Manager, Yokohama Resarch & Development Center, Technology & Innovation Headquarters*4Senior Engineer, Engine Engineering Department, Engine Division, General Machinery & Special Vehicles*5Manager, Engine Engineering Department, Engine Division, General Machinery & Special Vehicles

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 1 (March 2013)
50

compared with the required level of the conventional Tier 3 regulations. In addition, the EPA
Interim Tier 4 emission regulations newly employ NRTC (non road transient cycle) test, andtherefore require emission evaluation during not only steady operation, but also transient operation(Figure 2).
To respond to these regulations, MHI has created combustion chamber shape adjustment
technology, fuel injection control technology with CRS (electronic controlled common railsystem), EGR (exhaust gas recirculation) control technology for transient operation, and emission
after-treatment system control technology, and combined them to develop the D04EG engine incompliance with the EPA Interim Tier 4 emission regulations, which reduce the regulated
substances further than engines meeting the conventional regulations, while also attaining higher
fuel efficiency.

Figure 2

C1 steady test (left) and NRTC test (right)|2. D04EG engine specifications
Table 1 shows the specifications of the newly developed D04EG small diesel engine andconventional D04FR engine. The output per engine displacement of the D04EG has been enhanced
to attain lower fuel consumption than a conventional engine. Figure 3 compares the output and fuelconsumption between the newly developed and conventional engines. The newly developed engine
attains an approximately 5 to 8% reduction of fuel consumption compared with a conventional
engine by lowering friction loss through downsizing of the engine and other methods. In addition,the D04EG utilizes an external EGR system and emission after-treatment system for the reductionof emissions over the entire operating range of the engine.
Table 1

Specifications of engine certified Tier 3 regulations (D04FR) andengine certified Interim Tier 4 regulations (D04EG)

Engine model
Bore x strokemm
Number of cylinders
Engine displacement
LitersRated output / engine speed
kW/rpmMaximum torque / engine speed N・m/rpm
Fuel injection
Turbocharger
Exhaust gas recirculation
Dimensions L×W×H (*1)
mm
Weightkg

Certified Tier 3
D04FR
102×13044.2
74/2000
375/1600
Common rail
Turbocharger
Internal EGR
911×719×940
Approximately 410

Certified Interim Tier 4
D04EG
94×1204
3.3
74/2000
375/1600
Common rail
WG turbocharger
External EGR
879×689×848
Approximately 360*1 Sole engine dimensions excluding after-treatment system

Although the new devices shown above have been added, the newly developed engine
maintains dimensions equivalent to those of a conventional engine due to the downsizing of theengine itself (Figure 4), and therefore any required change of the space for mounting the engine ona vehicle is minimized.

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 1 (March 2013)
51

Figure 3 Comparison of engine performance between engine certified Tier 3 regulations(D04FR) and engine certified Interim Tier 4 regulations (D04EG)
Each item represents the relative value assuming that the value obtained with the D04FR at an engine speed of2000 rpm is 1.00.

Figure 4 Comparison of engine dimensions between engine certified Tier 3 regulations(D04FR) and engine certified Interim Tier 4 regulations (D04EG)|3. Technology for reduction of emissions
As emission reduction measures, the newly developed engine uses CRS and EGR, adjusts theshape of the combustion chamber, and features a DPF (diesel particulate filter (PM trap device)) for
the trap and reduction of PM emitted by the engine. MHI used numerical simulation andoptimization methods to work on the technological development efficiently in order to select anddetermine the specifications, operating conditions, and control methods of the emission reduction
measures. This section describes the details.

3.1

Fast adjustment of fuel injection pattern utilizing optimization methods

The employment of CRS and an external EGR system has made possible the fine control ofthe fuel injection pattern and oxygen concentration in the intake air in response to engine operatingconditions. CRS can arbitrarily control the number of injections, injection timing, and injection
amount (Figure 5). External EGR can arbitrarily adjust the oxygen concentration in the intake airby controlling the opening of the EGR valve. However, there are as many as hundreds of millionsof combinations, and the optimization of the injection pattern over the entire operating range can betime-consuming.

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 1 (March 2013)
52Figure 5 Fuel injection patterns and their effects

Therefore MHI utilizes optimization supporting tools to efficiently adjust multiple control
parameters in a short time. The use of a hybrid optimization method that combines an orthogonaltable test, a response surface model and an optimization method has made possible the selection of
the most appropriate control parameters in a short time in response to operating conditions.

3.2

Employment and control technology of EGR (exhaust gas recirculation system)

The D04EG newly employs an external EGR system to reduce NOx (nitrogen oxide)
formation in the combustion chambers. EGR returns some of the exhaust gas to the intake to reduce
the oxygen concentration in the combustion chambers. This lowers the combustion temperature,and consequently NOx formation can be suppressed.
For the efficient reduction of NOx formation through EGR, it is necessary to introduce EGR
gas into each cylinder evenly. To attain this, variation of the amount of EGR gas introduced
between cylinders is controlled by using numerical simulation and adjusting the shape of the EGR
introductory part (Figure 6).

Figure 6 Numerical simulation results for improvement of introductory part of EGR

Under operating conditions where the engine load changes transiently, such as the NRTCtransient evaluation mode newly added for the EPA Interim Tier 4 emission regulations, theamount of air in the combustion chamber becomes insufficient because of a delay in the responseof the turbocharger or other factors, and then the PM emission amount increases. In addition,
because the pressure difference between the intake and exhaust changes, the EGR introduction
amount can also change.
Therefore appropriate EGR introduction control in consideration of the delay in the responseof the turbocharger or other factors is required. The D04EG utilizes a control logic that uses anAFM (air flow meter) installed upstream of the compressor (turbocharger) for successive detectionof air flow and pressure, as well as temperature sensors at the intake manifold to momentarily
estimate excess air ratio (the ratio of actual air supply to the theoretical amount of air needed for
combustion). This can significantly suppress the increase of the PM emission amount byfeedback-controlling the EGR flow, so that the target excess air ratio is reached even in transientMitsubishi Heavy Industries Technical Review Vol. 50 No. 1 (March 2013)
53

operation. Figure 7 compares the results of a test on actual equipment between engines using theconventional open loop control and the newly employed feedback control. These results indicatethat the feedback control can reduce the PM emission amount under conditions of actual use.

Figure 7Reduction of PM due to feedback control

The feedback control can reduce the PM emission amount.

3.3

Combustion chamber shape adjustment through numerical simulation

The combustion chamber shape has been reviewed in order to reduce PM formation in thecombustion chambers. In the past, several types of combustion chamber shapes were determinedbased on previous test data, and then the best shape among them was selected through tests on
actual equipment. Because of the limited development period, however, the most appropriate shape
could not always be found. This time, optimization technology of the combustion chamber shapewith numerical simulation has been used, and then a combustion chamber shape that can further
reduce the PM emission amount could be determined earlier compared with the conventionalmethod. Figure 8 shows the numerical simulation results of the combustion chamber employed thistime. The combustion chamber shape and the fuel diffusion direction are optimized so that fuelinjected by the injector is widely distributed in the combustion chamber. As a result, the air inentire combustion chamber can be used effectively, and therefore the PM emission amount can bereduced.

Figure 8 Results of combustion chamber shape adjustment withnumerical simulation

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 1 (March 2013)
54

3.4

Emission after-treatment system and its control technology

The D04EG employs DPF to reduce the PM emission amount. Figure 9 illustrates anoverview of the emission after-treatment system of this engine. DPF taps PM emitted from theengine with a filter. As a result, the PM emission amount of the entire engine system can bereduced. When the temperature of the emissions is higher than a certain value, PM trapped by DPF
is regenerated continuously. However, if the engine is operated under conditions where the exhaustgas temperature is lower, PM accumulates in DPF, thus DPF regeneration that periodically burns
and removes the accumulated PM is required.
MHI has established technology that can accurately estimate the PM accumulation in DPF,
determine the timing of starting regeneration, and control the regeneration to prevent abnormal PM
combustion causing burning of DPF or unburnt PM. PM can be burnt by introducing
high-temperature emissions into DPF. The D04EG features a control system that raises the gas
temperature at the DPF inlet to approximately 600°C by implementing post-injection (fuel injection
during an exhaust stroke of the engine) in the combustion chambers, and allows unburnt fuel toreact with DOC (diesel oxidation catalyst).

Figure 9 Control system structure of emission after-treatment system|4. Conclusion
MHI has developed the D04EG small diesel engine in compliance with the EPA Interim
Tier 4 emission regulations, which reduce emissions further than conventional engines, while also
attaining lower fuel consumption. In the development of this engine, MHI was able to efficiently
optimize design and control parameters such as the combustion chamber shape and the fuelinjection pattern through utilizing not only emission reduction technologies including EGR andDPF, but also numerical simulation and optimization technology.
The D04EG has already acquired EPA Interim Tier 4 and EU stage3b certifications, and its
commercial production began in April 2012. It has also been verified on actual equipment that thisengine can be in compliance with the EPA Tier 4 emission regulations (which will become
effective in 2015) through the use of large-scale EGR, a variable flow turbocharger, and SCR(selective catalyst reduction) denitration technology.

References
1.
2.
3.
4.
5.

Takai et al., Tier3 Emission Certified Small Engines, Mitsubishi Juko Giho Vol. 46 No. 1 (2009) pp. 40-42
Satake et al., The Rapid Development of Diesel Engines Using an Optimization of the Fuel InjectionControl, Mitsubishi Heavy Industries Technical Review Vol. 45 No. 3 (2008) pp. 6-9
Yamada et al., Development of a Calibration Method for Optimum Operating Parameters of Diesel
Engines, Trans. of JSAE Vol.39 No.6 (2008) pp. 131-135
Imamori et al., Combustion Simulations Contributing to the Development of Reliable Low-Emission
Diesel Engines, Mitsubishi Heavy Industries Technical Review Vol. 48 No. 1 (2011) pp. 72-76
Hiraoka et al., The optimization method of DI engine parameters by KIVA, Trans. of JSAE Vol. 41 No. 1(2010) pp. 97-102