# Effect of Early Closing of the Inlet Valve on Fuel Consumption and Temperature in a Medium Speed Marine Diesel Engine Cylinder

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## Abstract

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_{x}in order to comply with the conditions of the MARPOL Convention, Annex VI. The reduction in NO

_{x}emissions will be achieved by the application of primary and secondary measures. The primary measures relate to the process in the engine, while the secondary measures are based on the reduction in NO

_{x}emissions through the after-treatment of exhaust gases. Some primary measures such as exhaust gas recirculation, adding water to the fuel or injecting water into the cylinder give good results in reducing NO

_{x}emissions, but generally lead to an increase in fuel consumption. In contrast to the aforementioned methods, the use of an earlier inlet valve closure, referred to in the literature as the Miller process, not only reduces NO

_{x}emissions, but also increases the efficiency of the engine in conjunction with appropriate turbochargers. A previously developed numerical model to simulate diesel engine operation is used to analyse the effects of the Miller process on engine performance. Although the numerical model cannot completely replace experimental research, it is an effective tool for verifying the influence of various input parameters on engine performance. In this paper, the effect of an earlier closing of the intake valve and an increase in inlet manifold pressure on fuel consumption, pressure and temperature in the engine cylinder under steady-state conditions is analysed. The results obtained with the numerical model show the justification for using the Miller processes to reduce NO

_{x}emissions and fuel consumption.

## 1. Introduction

_{x}emission limits for marine diesel engines with a rated power of more than 130 kW are divided into Tiers I, II and III according to the IMO (International Maritime Organisation). The limit values are applied depending on the date of construction date and the area of navigation, as shown in Figure 1.

_{x}emission limits are reduced by up to 21% compared to Tier I. Tier III requires an additional 76% reduction in emissions reduction for ships operating in ECA (Emission Control Areas). Depending on their operating area of navigation, many ships are affected by Tiers II and III. It is therefore necessary to optimize the emissions of marine diesel engines.

_{x}emissions are considerably lower. However, their efficiency does not exceed 48%. The advantages of medium-speed diesel engines are particularly pronounced in diesel-electric and hybrid systems. The slightly higher specific fuel consumption of four-stroke diesel engines can be compensated by utilizing waste heat of the exhaust gases and cooling water.

_{x}emissions are listed in Table 1.

_{x}emission reduction technologies, which are marked 1, 2, 7 and 8 in Table 1, have the most favourable impact on energy efficiency and specific fuel oil consumption (SFOC). The implementation of other listed technologies leads to an increase in specific fuel consumption.

_{x}emissions are largely temperature-dependent. By using modern electronically controlled fuel injection systems, this technology does not lead to a significant increase in specific fuel consumption.

_{x}emissions and a reduction in specific fuel oil consumption. To achieve the same engine power, the engine must be equipped with a turbocharger that supplies the same amount of air to the cylinder. More efficient (two-stage) turbochargers with higher pressure ratios are required.

## 2. Numerical Model of a Four-Stroke Diesel Engine

#### 2.1. Mass Conservation Law

_{in}is the mass of the medium entering the control volume and m

_{ex}is the mass of the medium exiting the volume, m

_{f}is the mass of fuel supplied and m

_{leak}is the mass of the medium exiting the volume. In a new or properly maintained engine, the leaked mass may be neglected.

#### 2.2. Energy Conservation Law

_{i,f}denotes heat released through fuel combustion and dQ

_{i,w}heat exchanged through the walls. The following variables indicate the sensible heat of the medium entering or leaving the control volume, the heat released by fuel combustion and conducted mechanical work. When the medium flows into the control volume, its enthalpy is added to the energy balance of the control volume; when it flows out, the enthalpy is subtracted.

#### 2.3. Indicated Work

_{c}in the cylinder is determined using the equation of state for a gas:

_{c}is derived from the crankshaft geometry:

_{S}is the cylinder swept volume, ε is compression ratio and λ

_{m}denotes the ratio between crank radius and piston stroke.

#### 2.4. Heat Exchange

_{1}and C

_{2}are the empirical coefficients and c

_{mps}is the mean piston speed.

#### 2.5. Heat Release

_{f}is the relative proportion of fuel burned, C is the constant that depends on the efficiency of fuel combustion. The index IS refers to the crankshaft angle at which ignition starts, while the index CD represents the duration of combustion. The exponent m is determined according to Woschni and Anisits [14]. The change in combustion duration Δφ

_{CD}is determined according to Betz and Woschni [15].

#### 2.6. Change in Mass and Excess Air in the Cylinder

_{AFR}is the stoichiometric mass of air in mixture with fuel.

#### 2.7. Working Medium Exchange in a 4-Stroke Engine Cylinder

_{p,geo}of the inlet and exhaust valves are determined according to the camshaft cam geometry. The flow coefficient αp is determined according to Chapman [19]. The flow function ψ for the subcritical pressure ratio is determined according to Bošnjaković [20]

#### 2.8. Turbocharger

_{T}is the flow coefficient, A

_{T,geo}denotes the cross-sectional area of the turbine, ψ is the flow function and p

_{EM}is exhaust manifold pressure.

#### 2.9. Effective Engine Power

_{M}is crankshaft speed in rpm.

_{mep}is the mean effective pressure and p

_{mip}is the mean indicated pressure. The mean effective pressure is determined by subtracting the mean pressure of the mechanical losses from the mean indicated pressure. The mean pressure of mechanical losses takes into account losses caused by friction and operation of oil and water pumps. In the developed numerical model, the mean pressure of mechanical losses is calculated using approximate expressions according to Maass [21].

## 3. Numerical Model Validation

#### 3.1. Referenced Engine Wärtsilä 12V50DF

#### 3.2. Model Validation

## 4. Analysis of the Impact of Earlier Inlet Valve Closing Angle

_{x}emissions and fuel oil consumption in the internal combustion engine. This measure can be applied to almost all engine types. Its positive effects are highlighted by the use of an efficient turbocharger. In the Miller process, an over-expansion process in the engine is achieved by shortening the compression stroke by closing the inlet valve earlier or later compared to conventional valve timing.

_{x}emissions and fuel oil consumption. Closing the inlet valve too early or too late with unchanged inlet manifold pressure results in poor cylinder filling which means that pressure and temperature are lower at the end of the compression stroke. Therefore, temperature and pressure in the high-pressure part of the process are also lower. Since the formation of NO

_{x}is exponentially related to temperature, even a small drop in temperature causes a significant decrease in NO

_{x}formation. The possibility of detonation combustion is also reduced.

_{x}emissions. Ust [28] compared the Otto-Miller, Diesel-Miller and Dual Miller processes. Gonca and Sahin [29] analyzed the influence of engine design and operating parameters on the performance of a turbocharged diesel engine running with the Miller process. Guan [30] and Tagai [31] investigated the possibility of combining the Miller process with other NO

_{x}reduction measures. Gonca [32] presented the detailed thermodynamic analysis of the dual Miller cycle for marine diesel engines. The results of the above-mentioned investigations were an additional motive for investigating the effects of early inlet valve closure on the performance of a medium-speed marine diesel engine. In the following, the results of the engine operation simulation using the developed numerical engine model are presented. The results obtained are compared with the values measured on the base engine, as displayed in Table 5.

#### 4.1. Simulation Results of Engine Performance with Early Inlet Valve Closing

_{x}formation. The simulation results for 50% and 75% of the maximum engine load show similar trends.

_{x}emissions while increasing the efficiency of the process, which is reflected in lower specific fuel oil consumption. It is also noted that the trend in specific fuel oil consumption is at a certain minimum and that the strategy of closing the inlet valves early has its limitations. This research was carried out with the intention of investigating the advantages of early closing of the inlet valves in an engine with an almost unchanged turbocharger configuration. The results obtained can be used as a solid basis for the simulation of engine performance with increased inlet manifold pressure, which can be achieved by using a highly efficient turbocharger.

#### 4.2. Simulation Results of Engine Performance with Increased Inlet Manifold Pressure

_{x}.

## 5. Conclusions

_{x}emissions. For the examined engine, specific fuel oil consumption is lowest when the inlet valves close between 20° and 40° earlier than in the base engine. Although this trend does not continue when the inlet valve closes 60° before the BDC, the specific fuel oil consumption is still lower compared to the base engine. Although it is theoretically possible to operate the engine even with the earlier closing angle of the inlet valves, the cam shape of the camshaft is the practical limitation.

_{x}emissions. At the same time, the increase in peak cylinder pressure does not exceed 15% even at maximum continuous engine power.

_{x}, but also on the reduction in specific fuel oil consumption.

## Author Contributions

## Funding

## Conflicts of Interest

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**Figure 12.**Maximum temperature in the engine cylinder and inlet manifold mean pressure depending on the inlet valves closing angle.

**Figure 13.**Closed indicated diagrams at different inlet manifold pressures at 100% of maximum engine load.

**Figure 14.**Change of mean temperature in engine cylinder at different inlet manifold pressures at 100% of maximum engine load.

NO_{x} Emission Reduction Technology | Expected Reduction | |
---|---|---|

1 | Two-stage turbocharger and Miller process | ~40% |

2 | Combustion process adjustment | ~10% |

3 | EGR—exhaust gas recirculation | ~60% |

4 | Higher humidity of the scavenging air | ~40% |

5 | Adding water to the fuel before injecting | ~25% |

6 | Direct injection of water into the cylinder | ~50% |

7 | SCR—selective catalythic reduction | ~80% |

8 | Replacing liquid fuel with gaseous fuel | ~85% |

**Table 2.**Data for the engine Wärtsilä 12V50DF [22].

Engine Parameter | Value |
---|---|

Bore, mm | 500 |

Stroke, mm | 580 |

Valves per cylinder (inlet/exhaust) | 2/2 |

Inlet/outlet valve diameter, mm | 165/160 |

Number of cylinders and configuration | 12 cylinders, V/45° |

Maximum continuous engine power, kW | 11,700 |

Engine speed, rpm | 514 |

Mean piston speed, m s^{−1} | 9.9 |

Number of turbochargers | 2 |

Turbocharger type | ABB TPL71-C |

**Table 3.**Manufacturer data for W 12V50 DF engine [22].

Engine Load | 50% | 75% | 100% |
---|---|---|---|

Engine power, kW | 5850 | 8775 | 11,700 |

Specific fuel oil consumption, g/kWh | 196 | 187 | 189 |

Exhaust gases temperature, °C | 337 | 336 | 352 |

Exhaust gases mass flow after turbocharger, kg/s | 13.9 | 18.4 | 23.0 |

Engine Load | 40% | 50% | 71% |
---|---|---|---|

Engine power, kW | 4680 | 5850 | 8307 |

Specific fuel oil consumption, g/kWh | 199 | 197 | 190 |

Maximum cylinder pressure, bar | 70 | 83 | 107 |

Exhaust gases temperature after turbocharger, °C | 412 | 392 | 359 |

Engine Parameter | Value |
---|---|

Bore, mm | 460 |

Stroke, mm | 580 |

Number of inlet/exhaust valves per cylinder | 2/2 |

Inlet/exhaust valve diameter, mm | 160/157 |

Inlet valve closing angle (° after BDC) | 26° |

Number of cylinders and configuration | 6 cylinders, inline |

Engine speed, rpm | 600 |

Mean piston speed, m s^{−1} | 11.6 |

Engine maximum continuous rating, kW | 7200 |

Number of turbochargers | 1 |

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Pelić, V.; Mrakovčić, T.; Medica-Viola, V.; Valčić, M.
Effect of Early Closing of the Inlet Valve on Fuel Consumption and Temperature in a Medium Speed Marine Diesel Engine Cylinder. *J. Mar. Sci. Eng.* **2020**, *8*, 747.
https://doi.org/10.3390/jmse8100747

**AMA Style**

Pelić V, Mrakovčić T, Medica-Viola V, Valčić M.
Effect of Early Closing of the Inlet Valve on Fuel Consumption and Temperature in a Medium Speed Marine Diesel Engine Cylinder. *Journal of Marine Science and Engineering*. 2020; 8(10):747.
https://doi.org/10.3390/jmse8100747

**Chicago/Turabian Style**

Pelić, Vladimir, Tomislav Mrakovčić, Vedran Medica-Viola, and Marko Valčić.
2020. "Effect of Early Closing of the Inlet Valve on Fuel Consumption and Temperature in a Medium Speed Marine Diesel Engine Cylinder" *Journal of Marine Science and Engineering* 8, no. 10: 747.
https://doi.org/10.3390/jmse8100747