Mitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
1Development of Diesel Engines for 2.0t to 3.5t and3.5t to 5.5t Forklift Trucks Complyingwith EU Stage V Emission Standards

TOMOHIDE YAMADA*1 TAKAYUKI YAMAMOTO*2MIZUKI KANAI*3

SHO NAKAMURA *4

YASUO KATO*1KAZUKI NISHIZAWA*5

For the development of D04EG engines, which comply with the European Stage V Non-RoadEmission Standards (EU Stage V emission standards), we improved the combustion and developed
a newly required DPF (diesel particulate filter) control. In order to produce a DPF control thatmeets market demands and evaluate the soot accumulation on the DPF, we acquired the actual
operation data of multiple engines available in the market and created an evaluation index based
thereon. We conducted verification with the created evaluation index and confirmed that reducing
soot can significantly lower the frequency of DPF regeneration and that DPF regeneration can becompleted during vehicle operation without interrupting work. We also conducted a field test andconfirmed that the desired functions were realized with actual vehicles in the market.

|1. Introduction
Mitsubishi Heavy Industries Engine & Turbocharger, Ltd. has developed andcommercialized engines that comply with the North American Tier 4 standards and we haveprovided customers with engines featuring excellent performance, reliability and low emission(1).
This time we have developed the D04EG engine, which complies with the EU Stage Vemission standards. The EU Stage V emission standards newly regulate the number of solid
particulates (PN: particulate number) in exhaust gas, in addition to the reduction of emissions bythe conventional exhaust gas regulations. To comply with the PN regulations, a DPF is practicallyindispensable and therefore DPF regeneration control for burning the soot accumulated in the DPF
due to engine operation is required. Depending on the DPF regeneration control method, it isnecessary to interrupt the work in order to perform DPF regeneration. For this reason, therealization of a DPF regeneration control that functions appropriately during normal engine
operation plays an important role in making the engine more convenient.

|2. Engine specifications
Table 1 lists the specifications of the engines that comply with the EU Stage V emission
standards. We have newly developed two engine models by adding the DPF required to be incompliance with the EU Stage V emission standards to engines that meet the North American Tier
4 standards. In order to improve the combustion to comply with the EU Stage V emission
standards, as well as to make it possible for the newly required DPF to be regenerated under any
engine operating condition including lower speed and lower load, the new engine adopts an exhaust
throttle valve. While complying with the EU Stage V emission standards, the developed engine
minimizes the effects of the DPF installation on the vehicle by allowing the DPF to be installed*1Chief Staff Manager, Engine Engineering Department, Engine & Energy Division, Mitsubishi Heavy Industries Engine &*2Chief Staff Researcher, Combustion Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

Turbocharger, Ltd*3Engine Engineering Department, Engine & Energy Division, E Mitsubishi Heavy Industries Engine & Turbocharger, Ltd*4

Engine Engineering Technology Development, Department Engine & Energy Division, Mitsubishi Heavy Industries Engine*5Chief Staff Researcher, Chemical Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

& Turbocharger, LtdMitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
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away from the engine, and is configured by adding only a DPF and an exhaust throttle valve
required for DPF regeneration to the North American- and Japanese-specification engines that do
not require a DPF.
We have developed cleaner and more convenient engines by realizing a DPF regeneration
control with high flexibility in addition to complying with exhaust gas regulations. This reportpresents the developed engine.
Table 1 Engine main specifications
Engine model name
Bore x Strokemm

4EG-NA

4EG-T

94×12094×120

Number of cylinders―44Displacement

Liter

3.3

3.3

36/2250

54/2250

Rated output/ speed

kW/min-1-1

Maximum torque/ speed

N・m/minFuel injection system―

Aspiration method―

Exhaust gas recirculation
Exhaust gas aftertreatment
device―Externally cooled EGR

Externally cooled EGR―

Diesel particulate filter

Diesel particulate filter

Remarks

177/1800
260/1800
Electronically controlled common rail Electronically controlled common railsystemsystemNaturally aspirated
WG supercharged

The following changes were made to comply with the EU Stage V emission
standards from the engine models that meet the North American Tier 4
standards.
- Change of the exhaust gas aftertreatment device to a diesel particulate filter(DPF).
- New adoption of an exhaust throttle valve for DPF regeneration.

|3. Technologies for complying with EU Stage V emission standards
To be in compliance with the EU Stage V emission standards, a DPF is required in order tomeet the PN regulations. The soot collected inside the DPF needs to be burned off (DPFregeneration) when a certain amount accumulates and it is desirable to reduce the frequency of DPFregeneration. Therefore, we worked on the reduction of soot emission from the engine and at thesame time, made it possible to regenerate the DPF under any conditions during engine operation torealize a control that does not require the interruption of work in order to perform DPFregeneration.

3.1

Reduction of soot emission for reduction of DPF regeneration frequency

In order to reduce the frequency of DPF regeneration, it is necessary to reduce the particulate
accumulation speed and the most effective measure is to suppress the generation of soot in thecombustion chamber, which accounts for most of the particulates. In the combustion process of adiesel engine, soot starts to be generated in a low oxygen concentration region at the center of thefuel injection immediately after ignition, reaches a peak during combustion and then mixes with air
in the latter half of oxidization, which leads to re-oxidization. Therefore, key points for reducing
soot emission are to take in a large amount of air during fuel injection before ignition to suppress
soot oxidization immediately after ignition and to promote mixing in the latter half of combustion
to accelerate soot re-oxidization. This time, we achieved these goals by increasing the number ofthe injector nozzle holes and reducing their diameter and by improving the shape of the combustion
chamber. This was done by using combustion simulation. The development was carried out while
determining the specifications through theoretical investigation using the simulation and thenconfirming them through tests. Figure 1 (a) presents the simulation results of improving the shapeof the combustion chamber. It is indicated that, before the shape improvement of the combustion
chamber, the fuel is distributed unevenly therein and after the improvement, on the other hand, it isdistributed throughout the combustion chamber and mixes well. Figure 1 (b) gives the confirmation
results obtained by an engine test using a combustion chamber with a shape determined by thissimulation. It was confirmed that the soot was significantly reduced.
In order to reduce the frequency of DPF regeneration in the actual market, it is necessary toreduce soot emission in consideration of the transient behavior of the operating patterns used in themarket. In this development, we carried out evaluations using multiple operating patterns preparedMitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
3in advance. Figure 2 is an example of the evaluation pattern. It is indicated that the soot emission
was reduced significantly by the improvement. As a result, the DPF regeneration interval in anormal usage environment was extended to more than twice that of the conventional one.

Figure 1 Reduction of soot emission amount due to improvement of combustion chamber
shape

Figure 2

3.2

Evaluation of soot emission amount under in-market operating conditions

DPF regeneration control

DPF regeneration burns off soot accumulated inside the DPF for removal. For that purpose, itis necessary to control the exhaust gas temperature at a predetermined value to ensure anappropriate soot oxidation rate. In terms of controlling the exhaust gas temperature, it is favorable
to install the DPF near the engine. On the other hand, installing the engine and DPF separately canmake the equipment layout flexible. The developed engine and DPF can be installed separately inorder to allow existing machines and vehicles to be easily equipped with an engine that complies
with the EU Stage V emission standards. It was confirmed that good temperature control can beperformed without being affected by the response delay due to the pipe length under any operating
condition and that problems such as the fuel for DPF regeneration becoming excessive and being
discharged in exhaust gas as-is and the exhaust gas temperature rising abnormally due to responsedelay, do not occur.
The exhaust temperature control for DPF regeneration is handled by adding and adjusting thefuel injection into the cylinder so that the temperature rises and by throttling the exhaust gas withthe exhaust throttle value. The exhaust temperature at the DPF is adjusted so as to be maintained at
the required constant temperature level regardless of the steady or transient operating conditions
over a wide range of engine loads and engine speeds. In particular, by using the exhaust throttle
value, it is possible to maintain the exhaust temperature required for DPF regeneration, including in
low load and low speed regions.
As a result, we have established a control that can perform regeneration under almost all
operating conditions as long as the engine is running after warming up and can complete DPF
regeneration automatically while the engine is in use.

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
4|4. Evaluation under actual operating conditions
Since our industrial engines are used for various applications, we carried out thedevelopment so that DPF regeneration can be completed under any operating pattern. There arecharacteristic operating patterns depending on the application, so we investigated, in particular, theactual operation conditions of the forklift trucks to which the developed engine is to be installed
and the evaluation of DPF regeneration was carried out on the engine bench and in the market.

4.1Engine evaluation with evaluation patterns based on in-market operation data

In order to evaluate that DPF regeneration can be completed under any conditions without
interfering with normal engine use, we conducted a preliminary survey of engine operating
conditions in the market. The engines developed this time are to be installed in forklifts inparticular, so the survey was conducted with the cooperation of Mitsubishi Logisnext Co., Ltd. We
asked customers who actually use forklifts in their daily work to use forklifts equipped with anengine data logger in order to measure the engine operating status.
The operating status survey was conducted for multiple forklifts and customers, including
every-millisecond-measurement of multiple data points on engine operating conditions such asengine speed, throttle opening, fuel injection quantity, engine coolant temperature and operating
environment temperature. We acquired data for more than hundreds of hours of operating time intotal. The data was analyzed focusing on the engine speed and fuel injection quantity (engine load)and characteristic operating patterns were identified and extracted. The acquired operation data wasclassified into extracted operating patterns according to the characteristics and the occurrence
frequency of each operating pattern during actual operation in the market was arranged. Figure 3
shows an example of actual operation data and the classification into operating patterns. By
combining the operating patterns in proportions corresponding to their occurrence frequency, aDPF regeneration evaluation pattern that reflects the operation status in the market was created andused for evaluation on the engine bench. Figure 4 is a DPF regeneration evaluation pattern createdby combining the extracted operating patterns.

Figure 3

Analysis example of in-market operation data

We evaluated the engine operable time without DPF regeneration on an engine bench using
multiple evaluation patterns including the created evaluation pattern. It was confirmed that the sootreduction implemented this time effectively reduced the required number of DPF regenerations perunit operating time to as little as less than half that of the conventional model. It was also
confirmed as expected that DPF regeneration can be completed under any engine operating

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 2 (June 2021)
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condition for multiple evaluation patterns including actual operating patterns in the market focusing
on low speed and low load. Figure 5 is an example in which it was confirmed that the exhaust
temperature could be maintained constant at the required level and DPF regeneration was possible
for the evaluation pattern.

Figure 4

Example of evaluation pattern based on in-market operation data

Figure 5

Exhaust temperature control in DPF regeneration based on evaluation pattern

4.2

Verification with field follow-up

Also with the cooperation of Mitsubishi Logisnext Co., Ltd., we installed an engine datalogger on vehicles before their release and asked European customers to use them in the field inorder to verify that the desired functions were realized. In advance of long-term operation in
Europe, we prepared a system to monitor the local operation status on a computer in a domestic
office with the data logger signal uploaded to the server via mobile phone line. We have checked
the operating status data on multiple vehicles for several thousand hours in total and some vehicles
are still operating today.
This verification checked the data under the actual operating conditions in the market

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focusing on [1] whether DPF regeneration could be completed under any operating condition and[2] whether the DPF regeneration interval was as long as expected.
It was confirmed by checking all the operation data that—also under actual operating
conditions—DPF regeneration could be continued and completed under any operating condition
except when the customer stopped the engine during operation and that there was no interruption ofwork for DPF regeneration. It was also confirmed that even when the engine was stopped during
DPF regeneration, it could be resumed and completed without any problem after restarting theengine.
As a result of checking the total operating time and the number of times of DPF regenerationfor each forklift, it was confirmed that the operating time until the moment when DPF regeneration
was required was also the same as that obtained on the engine bench with the evaluation pattern inthe development and that the DPF regeneration interval was extended to more than twice that of theconventional model.

|5. Conclusion
For the adoption of DPF for engines to allow them to comply with the European Stage V
emission standards, we carried out development aiming at reducing soot to extend the DPF
regeneration interval and expanding the DPF regeneration range. In the evaluation of the developed
engine, we incorporated evaluation patterns created based on the operation data measured in themarket in addition to the existing evaluation methods, confirming that the target functions wereachieved.
The developed engines have been mass-produced since 2020. We will continue to develop
engines that consider actual market conditions and are convenient and attractive for customers.

References(1)

Hiraoka et. Al., Development of EPA Interim Tier 4 Certified Small Diesel Engine, Mitsubishi Heavy
Industries Technical Review, Vol.50 No.1 (2013) p.60～65