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Hard Target


Emissions regulations that focused on mitigating NOx and particulate matter (PM) got underway in 2000. From then, they became increasingly stringent, with Tier 4 commencing in 2013, requiring a further 37% reduction in NOx and a 90% reduction in PM. Moreover, previous tiers were based on a determined number of revs and load; however, with Tier 4 it was based on the transient cycle. This means that an engine still has to meet the standards, regardless of the altitude, climate or region. 

For Yanmar’s innovative three-step regeneration solution, a diesel particulate filter (DPF) was on the cards from the start. However, due to many problems occurring with DPFs, there were many things to take into consideration. Essentially, the DPF collects the soot, resulting in cleaner emissions, and periodically that soot needs to be burnt or disposed of. When the excess soot needs to be disposed of the engine must stop, resulting in a reduction in productivity. In the case of burning  the soot, fuel needs to be sent through the DPF, resulting in additional fuel usage. 

Yanmar’s concept was to introduce an automatic step at roughly 350°C, the stage at which the soot would typically be incinerated with previous DPFs. Without the need for fuel injection, soot is periodically disposed of, and by utilizing ‘reset regeneration’ at 100-hour intervals, all soot is completely disposed of. On the remote chance that the filter gets clogged, in conjunction with fuel injection, regeneration can be performed manually. The success of Yanmar’s Tier 4 engine led directly to the capability of Yanmar’s mini-construction equipment being maintenance free with a product life of 6,000 hours. 

Further enhancements

Development of this engine wasn’t exactly smooth sailing, though. Initially, Yanmar used its own multi-point (MP) fuel injection system, until development hit a wall. Five years after development had begun in February 2009, the team made the decision to switch from MP to a common rail system. For the engine control unit (ECU) side of the project, Yanmar teamed up with an engineering company to collaborate on technology development. This decision put Yanmar back two years in the development stage, compared with its competitors. 

But while it may have incorporated technology from other companies in the engine’s design, this on its own wasn’t what led to Yanmar’s success. It established a new facility for research that furthered its knowledge in this area. Additionally, in
relation to the manufacturing processes, right from the design phase, Yanmar was going to the sites where the engine would
be used, and making improvements on any problems that had unfolded. 

In the development stage, Masashi Sagara of the planning division visited customer work sites and monitored the progress made. Through collaboration with sales, they were performing real tests on site with the engines. Engines were installed in a wide range of machines, with more than 250 machines being monitored. Moreover, development, manufacturing and sales collaborated closely throughout the project. 

What we like to call a Yanmar engine

This hard work led to Yanmar’s solution being the world’s first California Air Resources Board-certified Tier 4 engine.
The first of the engines was shipped out in 2012, and as we went to press, some 70,000 have been shipped – and not a
single DPF has gotten clogged up yet. Also, fuel consumption has been shown to beat one of its major competitors by an
impressive 7.5%. 

While Yanmar did have to give up on its own fuel-injection system, from the perspective of DPF controllability and fuel efficiency, it has succeeded once again in making a top-of-the-range product. Some 200 employees were involved in the project, and when you factor in all the people who were involved where the engines were tested, that figure adds up to about a thousand expert workers. “Never before have I seen unity at that scale,” says Ryo Yuki of Yanmar’s testing division. “Using the Tier 4 as a stepping stone, hopefully we can all come together again and work on something big one more time.” 

Tier 4 engine and philosophy

With Yanmar’s innovative three-step regeneration process, soot – the DPF’s biggest problem – has been resolved. This was achieved through leveraging automation, which has now enabled the 6,000-hour lifespan of mini-construction equipment to be maintenance-free. Compared with the non-DPF-equipped engine of one of its major competitors, Yanmar’s amounts to a 7.5% improvement in fuel efficiency. “To conserve fuel is to serve mankind,” says the company. While Yanmar delivers innovative change in technology, its philosophy of conserving fuel will always remain the same. 

The new TNV engine series

Yanmar’s new TNV engine series was developed to satisfy customer demand while complying with strict emission regulations. Its advanced combustion technology using a common rail injection system and cooled exhaust gas recirculation (EGR), which is controlled by a unique correction method, are used to achieve better engine performance, with an exhaust aftertreatment system being adopted for cleaner emissions. A total engine management system using Yanmar’s original software maintains optimal engine performance by itself, by adjusting the engine operating parameters automatically based on physical models. It also helps to achieve reliable DPF regeneration using a unique regeneration strategy without changing the feel of engine operation. It additionally has the advantage of enabling very flexible designs.

The new TNV engine series comprises products developed to be even cleaner than before, without impairing the fuel consumption, high power, reliability and low noise performance that were characteristic of the previous models. Innovations have been introduced not only to hardware, but also to software, achieving high performance suitable for the engine operating conditions and environment. The selection of optimum devices and maintaining the same engine sizes as previous models provides flexibility for installation in a wide range of operating machines, and makes replacing previous model engines with the new one easy. The new TNV engines are offered with outputs from 6-56kW to meet a wide range of customer needs. 

 TNV Engine  
An overall view of a new TNV engine Fig. 1: The new TNV engines are offered with outputs from 6-56 kW 

A DPF is used as an exhaust aftertreatment system to maintain clean emissions and good operability in high load ranges, at which PM emissions from the engine increase. However, when the DPF accumulates PM from the exhaust gas, the exhaust pressure rises and excessive EGR is performed, causing the PM amount to increase. For this reason, the EGR ratio must be controlled to an appropriate level to reduce the risk of DPF clogging and the frequency of DPF regeneration. Also, because the allowable time to stop operations for DPF regeneration is limited in industrial machinery, there is a need to perform reliable regeneration while the engine is in use. Further, as an industrial engine, the same flexibility as in previous models is required to enable installation in a wide range of operating machines with different layouts. 

To meet these requirements, Yanmar adopted new devices and an innovative control software. Its original total engine
management system calculates the conditions of engine and components based on a physical model to perform the optimum engine control according to the operating conditions. Installing this control system in the ECU has reduced the risk of DPF clogging and the regeneration frequency, as well as emissions. Further, the adoption of a control system that does not use an air flow sensor eliminates the man-hours required for making adjustments for each layout, making it easy to install the engine in operating machines. 

 Evaluation results
Fig. 2: Evaluation results of PM and NOx + non-methane hydrocarbons (NMHC) emissions
Fig. 3: The results of an evaluation of the EGR ratio, NOx and smoke in the case of high exhaust pressure and low atmospheric pressure (high-altitude conditions)

Figure 2 shows the evaluation results of PM and NOx + non-methane hydrocarbons (NMHC) emissions. Emissions from the 4TNV88-B engine, which is certified by the Environmental Protection Agency for Tier 3 regulations, exceed the Tier 4  regulation limit. NOx+NMHC emissions are reduced using a common rail injection system and cooled EGR without an increase in PM emissions with 4TNV88C. PM is reduced to a tenth of the previous level by employing a DPF system. As a result, the new TNV engine series have achieved the strict Tier 4 regulation values. 

In the 19-37kW output range, this engine is the first in the world to acquire certification for complying with the particulate number (PN) regulations enacted by Switzerland. It should be noted that the introduction of PN regulations in the Stage V regulations, due to come into effect from 2019, is currently under discussion in Europe. As of 2013, Yanmar’s new TNV engine series had the potential to comply with these regulations. 

Product strengths

In engines equipped with a DPF, when the exhaust pressure rises due to PM accumulation as previously described, or when atmospheric conditions change, the EGR gas amount must be controlled to an appropriate level to maintain DPF quality. Figure 3 shows the results of an evaluation of the EGR ratio, NOx and smoke in the case of high exhaust pressure  and low atmospheric pressure (high-altitude conditions). As the exhaust pressure and atmospheric pressure change, the EGR gas flow is controlled to an appropriate level by Yanmar’s original engine control, and by restricting the increase of smoke, the DPF clogging risk and regeneration frequency are reduced. Yanmar’s three-step regeneration control system comprises assist regeneration, which does not use postinjection; reset regeneration, which uses post-injection; and stationary regeneration, which stops work to perform complete regeneration. This control enables regeneration even in low-speed, low-load operations where DPF regeneration has usually been difficult. 

Flexibility for installation

In the control described above, it is important to control the EGR to an appropriate level and measure the air intake flow to perform reliable regeneration. Air intake flow measurement is usually performed in automobile engines with an air flow sensor. However, the air flow sensor tends to be affected by the air intake layout, requiring adjustments to be made for each layout. In an industrial engine that requires installation in a wide variety of operating machines, these adjustments require many man-hours, presenting a major obstacle to installation. 

Yanmar released the new TNV engine series to the market in 2013, and since then it has been highly rated by customers. At present, industrial engines face an ever-changing environment, with emission regulations becoming stricter and operating machines becoming even more advanced. In the future, Yanmar will continue to seek value from the perspective of its customers and continue in its efforts to provide them with the most optimal solutions.

Note: this article has appeared in iVT International Off-Highway magazine.

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