YANMAR Technical Review

Abstract

Yanmar developed the 6GY135 engine as a successor to the 6KXZ Series for marine and industrial diesel applications. This engine features a common rail system to meet emission regulations in Japan, Europe, U.S., and China. The design concepts included maximizing customer life cycle value and minimizing environmental impact. The engine achieves clean exhaust emissions and excellent low fuel consumption while maintaining reliability.
Market research and Smart Assist analysis were used to verify quality requirements, which were then reflected in the design and control system. A thorough overhaul of past models was also carried out to improve quality.
Under EPA Tier 3 regulations for North America, the engine provides up to 7% more torque than competing models, while reducing exhaust emissions and greenhouse gases. The engine is more compact and lighter in weight, with optimal specifications determined by using model-based development (MBD) to analyze combustion parameters, thereby shortening the development period and meeting diverse needs.

1. Introduction

Yanmar has developed the new 6GY135 Series of common rail diesel engines as a successor to the 6KXZ Series for marine and industrial applications.
Marine engines are used not only in large container and tanker vessels, but also in smaller commercial fishing and pleasure boats.
The 6GY135 Series is intended for this latter market and was designed based on the concepts of maximizing customer life cycle value and minimizing environmental impact. The engines are equipped with common rail injectors for clean exhaust and easy starting, with advances in fuel consumption and torque performance achieved without compromising the reliability that was a feature of previous models.

2. Use of MBD to Maximize Lifecycle Value and Minimize Environmental Impact

While the previous 6KXZ Series earned a strong reputation in the market for its excellent reliability as a marine and industrial engine, measures for reducing greenhouse gases (GHGs) and rapid rises in fuel prices over recent years have driven demand for lower fuel consumption. Accordingly, the new engines were designed to achieve even lower emissions and better fuel economy. Unfortunately, pursuing one or other of these objectives in isolation risks compromising reliability and making fuel consumption or emissions worse. For this reason, the project utilized model-based development (MBD) to satisfy both requirements simultaneously while still bringing the new engine to market rapidly.

2.1. Use of Smart Assist to Identify Customer Quality Requirements

To identify the life cycle value requirements for the engines from customer feedback, an analysis was conducted of Smart Assist big data obtained from working engines. The results were then used to define the engine performance requirements in quantitative terms (Fig. 1). Smart Assist is a service that prioritizes customer peace of mind and convenience, with features that include management tools for tracking information on engine operation.
The analysis conducted using this service functionality found that the 6KXZ Series suffered from poor acceleration performance due to the engine torque curve lacking the leeway relative to the actual operating curve in the low-speed range needed for acceleration, and that exhaust emissions (smoke) increased when this occurred. This made the vessel handling feel worse and degraded product performance due to the risk of smoke damage to cargo. Accordingly, in developing the new engine, Yanmar utilized a wide range of data from actual operation to determine the quality requirements, specifically engine torque characteristics and exhaust gas concentration, that would be needed to provide the smooth and powerful acceleration that customers are demanding (Fig. 2).

2.2. How Combustion Performance for GHG Reduction was Achieved

The combustion performance of a diesel engine is determined by a complex mix of factors, including the geometry of the combustion chamber, injector specifications, and intake and exhaust systems. Accordingly, the engine development project followed the steps shown in Fig. 3 to rapidly identify the combustion requirements needed to achieve the engine performance quality specified in section 3.1. The first step was to use a 1D performance simulation to determine the intake and exhaust system parameters, including valve timings and turbocharger characteristics. The data obtained by this work was then used in a 3D combustion simulation to determine additional parameters, including piston geometry and injector specifications. By doing so, this desktop analysis identified the combination of specifications that would deliver optimal combustion performance. To provide a quick assessment of the analysis results, agreement between simulation and reality was verified experimentally using a single-cylinder test engine. Further testing was then conducted on a six-cylinder engine.
To maintain the reliability for which the 6KXZ Series has such a strong reputation, a reliability analysis was undertaken using boundary conditions for things like the thermal load on the pistons determined based on the combustion performance obtained from the desktop analysis. This work was then verified using the single-cylinder test engine to ensure that development was able to proceed with minimal rework of the early stages of design.

2.3. Acceleration Matching Using Coupled Simulation

Acceleration matching was an important consideration for increasing sales of the 6GY135 Series for use in pleasure boats, a market not targeted by the previous 6KXZ Series engines. Fig. 4 shows an example of how matching is done when evaluating pleasure boat acceleration to ensure that it matches what customers are looking for. Here, a system for the desktop evaluation of vessel acceleration behavior was put together by combining the 1D engine model from section 3.2 with a vessel model and ECU model built using Simulink. The right side of Fig. 4 shows an example from this work of a desktop study of the influence of different propellors on the acceleration profile.
These results demonstrated that it was possible to conduct highly accurate desktop assessments of how an actual vessel will accelerate based on factors such as propellor specifications and clutch settings that in the past would have relied on people with specialist experience. By doing so, the development achieved both good acceleration performance and exhaust color in only a small number of design iterations.

3. Engine Performance

3.1. Achieving Class-Leading Fuel Efficiency in Japan and Overseas Markets

The engine for the Japanese market has fuel consumption that beats that of competitors by more than the 6% threshold for recognition as an energy-efficient product in terms of the four-mode fuel consumption criterion specified by the Fishing Boat and System Engineering Association of Japan. This means that it is possible to apply for designation as an energy-efficient product, even when converting from a competing or older model engine.
Furthermore, some of the engines intended for overseas markets have a rated fuel consumption that is 5% to 9% lower than that of competitors while also complying with the U.S. EPA Tier 3 and general marine IMO Tier 2 emission standards.

3.2. Combining Reliability and High Output with Emissions Compliance

Model P in the 6GY135 Series of engines for the Japanese market features class-leading output, smaller size, and lighter weight than its predecessor, despite having the same bore and stroke (Fig. 6).

By switching from mechanical fuel injection to a common rail system, the new engine now has emissions low enough to satisfy the IMO Tier 2, IMO Tier 3, EPA Tier 3, and China Tier 2 emission standards, with the lineup having expanded from the previous model’s three Japanese-market variants to a total of 35 variants for both Japan and overseas markets. This means that Yanmar can deliver an optimal solution that suits the customer’s circumstances (Fig. 7).

4. Conclusions

Looking ahead, Yanmar has identified reducing GHG emissions as a focus for further research and development. Building a sustainable future demands both technological innovation and practical action. Using this latest development as a platform, Yanmar intends to redouble its efforts to contribute both to life cycle value and reducing environmental impact.