**2. Materials and Methods**

This section describes the engine analyzed and the numerical model employed to study the performance and emissions.

### *2.1. Description of the Engine Analyzed*

As mentioned above, the engine analyzed is theWärtsilä 6 L 46 (Wärtsilä Corporation, Finland)[34,35], diesel, six-cylinder, four-stroke, water-cooled, and turbocharged. Each cylinder of this engine has two intake and two exhaust valves and a fuel injector with 20 holes is situated at the center of the cylinder head. This is a direct injection engine, i.e., the fuel is injected directly into the cylinder. The injection pump provides injection pressures up to 1500 bar. Optionally, this engine includes the possibility to incorporate direct water injection (DWI) to incorporate water at 400 bar from an external pump unit to each injection. The injector is thus equipped with a dual nozzle with separate needles for water and fuel. This system was employed in the numerical model to simulate water or ammonia injection.

In the present work, a comprehensive analysis was performed in a Wärtsilä 6 L 46 installed on a tuna fishing vessel. Many parameters were characterized at di fferent loads, such as in-cylinder pressure, consumption, indicated and e ffective power, scavenging air pressure and temperature, exhaust gas pressure and temperature, lubricating oil pressure and temperature, cooling water temperature, emissions, etc. Although this engine is designed to operate under heavy fuel oil, marine diesel oil operation is also possible. Since these data were taken on board and near the coast, marine diesel oil was employed. The viscosity and density of this fuel are 12.5 mm<sup>2</sup>/s and 885 kg/m<sup>3</sup> at 15 ◦C and its sulfur content 0.89%. For instance, Figure 1 indicates the results of the in-cylinder pressure along the operating cycle, at 100% load. The engine performance analyzer MALIN 6000 was employed to characterize the in-cylinder pressure. This pressure transducer is connected to the bleed valve, located at the engine head, which acts as an indicator channel. It worth mentioning that the experimental pressure trace can be distorted due to pressure waves in the channel [36], and that no algorithm was applied to correct this drawback.

**Figure 1.** In-cylinder pressure at 100% load, experimentally measured.

Other experimental data at di fferent loads are indicated in Table 1. In particular, the speed, power, mean indicated pressure (MIP), maximum pressure, specific fuel consumption (SFC), and emissions. NOx, CO, HC, and CO2 emissions were analyzed using the Gasboard-3000 series (Wuhan Cubic) gas analyzers, particularly Gasboard-3030 for HC and Gasboard-3000 for NO, CO, and CO2. The load, speed, and SFOC were taken from the engine monitoring system.


**Table 1.** Experimental data.
