The present work aims at analyzing the fluid dynamic efficiency of a four-stroke spark-ignition engine. Specifically, a production four-cylinder internal combustion engine has been investigated during the intake and exhaust phase. The experimental characterization has been carried out at the steady flow rig adopting the dimensionless flow and discharge coefficients. The analysis has highlighted the great influence of the valve lift on the volumetric efficiency of the intake and exhaust system. Furthermore, the global investigation has demonstrated that the throttle angle has a significant influence on the head permeability during the induction phase. Particularly, the throttling process effect increases with the valve lift. Finally, the work has shown that all experimental data can be correlated by a single curve if an opportune dimensionless plot is adopted.

A deep knowledge of the intake and exhaust processes is fundamental to design and optimize modern internal combustion engines (ICEs). The development of efficient intake and exhaust systems, in fact, plays a basic role both to reduce exhaust emissions and fuel consumptions and to improve the performances of actual engines [

To this purpose, different investigation tools, based on CFD codes [

These analyses are based on dimensionless discharge and flow coefficients [

The aim of the paper is the analysis and the characterization of the fluid dynamic behaviour of a production spark-ignition engine during the intake and the exhaust phase. A four-stroke internal combustion engine was examined at a steady flow rig in order to have detailed information on the global volumetric efficiency of the engine.

The influence of the valve lift and throttle valve opening on the head breathability was investigated adopting the discharge and flow coefficients. In fact, few quantitative studies on the effect of the throttling process on engine volumetric efficiency are available in the literature, in spite of the great influence of the throttle opening on the engine fluid dynamic efficiency. Finally, a dimensionless plot was used to correlate experimental data.

The experimental analysis focused on a production spark-ignition engine. Figure

Main engine characteristics.

Engine | Four-stroke spark-ignition |
---|---|

Number of cylinders, | 4 |

Number of valves per cylinder, | 2 |

Stroke/Bore, | 1.167 |

Intake valve diameter/Bore, | 0.461 |

Exhaust valve diameter/Bore, | 0.387 |

Engine head.

Measurements were carried out setting the pressure drop at

Table

Measuring conditions.

Analysed system | Intake | Exhaust |
---|---|---|

Pressure drop, | 10 kPa | 10 kPa |

Dimensionless valve lift, | 0.060 ÷ 0.301 | 0.072 ÷ 0.358 |

Throttle angle, | — |

The discharge and flow coefficients were used to define the global fluid dynamic efficiency of the intake and exhaust system [

The difference between the discharge and flow coefficient lies in the definition of the reference area

Furthermore, absolute flow coefficients

Moreover, mean flow coefficients were calculated in line with Li et al. [

The overall uncertainty of dimensionless flow coefficients and absolute flow coefficients was always lower than 3%, and it decreased with valve lift and throttle angle.

Figure

Influence of valve lift on flow (a) and discharge (b) coefficients. Intake phase—Wide open throttle (WOT) configuration.

Figure

Absolute and mean flow coefficients for the intake system-WOT configuration.

Analysed system | Intake |
---|---|

Throttle angle, | 90° |

Absolute flow coefficient, | 0.291 |

Absolute discharge coefficient, | 0.469 |

Mean flow coefficient, | 0.330 |

Mean discharge coefficient, | 0.427 |

Maximum flow coefficient, | 0.376 |

Maximum discharge coefficient, | 0.559 |

Influence of cam angle on flow (a) and discharge (b) coefficients. Intake phase—Wide open throttle (WOT) configuration.

At the same time, the fluid dynamic behaviour of the exhaust system has been evaluated. To this purpose, the flow from the cylinder through the exhaust valve has been characterized (Figure

Influence of valve lift on flow (a) and discharge (b) coefficient. Exhaust phase.

The figure depicts a continuous increase in the flow coefficient when the valve lift increases, because of the progressive raise in the exhaust mass flow rate. A plateau is found for

The two dimensionless coefficients versus the cam angle for the exhaust system are plotted in Figure

Absolute and mean flow coefficients for the exhaust system.

Analysed system | Exhaust |
---|---|

Absolute flow coefficient, | 0.359 |

Absolute discharge coefficient, | 0.458 |

Mean flow coefficient, | 0.426 |

Mean discharge coefficient, | 0.448 |

Maximum flow coefficient, | 0.522 |

Maximum discharge coefficient, | 0.515 |

Influence of cam angle on flow (a) and discharge (b) coefficient. Exhaust phase.

In order to investigate the influence of throttling process on the intake system breathability, the global analysis was also performed at several throttle angles (Figure

Influence of throttle angle on head permeability in terms of dimensionless flow (a) and discharge (b) coefficient. Intake phase.

Experimental data put in evidence similar behaviours for the different throttle positions and the presence of the three flow regimes. It is possible to observe that the “transition” from a flow condition to another one is reached at lower valve lift values when the flow is throttled. As an example, the transition phenomena for the wide-open throttle configuration (

In addition, the plot illustrates the noticeable influence of the throttle valve opening on the volumetric efficiency of the intake system. As expected, a progressive increase in the head permeability is observed when the throttle angle upsurges. However, this effect tends to reduce significantly with the throttle angle and there are small effects on the fluid dynamic efficiency of the intake system when

Percentage difference in dimensionless flow coefficients between WOT and throttled configurations. Intake phase.

This trend is also visible in Table

Influence of the throttle angle on the absolute and mean flow coefficients. Intake system.

Throttle angle, | 90° | 70° | 50° | 40° | 30° |
---|---|---|---|---|---|

Absolute flow coefficient, | 0.291 | 0.289 | 0.277 | 0.246 | 0.185 |

Absolute discharge coefficient, | 0.469 | 0.466 | 0.448 | 0.407 | 0.321 |

Mean flow coefficient, | 0.330 | 0.328 | 0.313 | 0.253 | 0.202 |

Mean discharge coefficient, | 0.427 | 0.424 | 0.406 | 0.373 | 0.272 |

Maximum flow coefficient, | 0.376 | 0.372 | 0.355 | 0.304 | 0.217 |

Maximum discharge coefficient, | 0.559 | 0.553 | 0.537 | 0.507 | 0.459 |

Dimensionless flow (a) and discharge (b) coefficients contour plot. Intake phase.

Finally, all the experimental data were correlated by adopting a new dimensionless plot, defined in a former work [

Figure

Universal trend in the dimensionless flow coefficients. Intake phase.

The result is very useful because it guarantees a drastic reduction in the measurements that have to be done to characterize the fluid dynamic efficiency of the engine intake system. As a consequence, time and costs of the investigations are decreased. At the same time, plotting the experimental data in the suggested form facilitates the check during the measuring phase. Obviously, further analysis should be performed to verify the extensibility of the previous law to other engines.

An experimental investigation was performed to analyse the fluid dynamic efficiency of a production internal combustion engine during the intake and the exhaust phase. Specifically, the attention was focused on a multicylinder spark-ignition engine.

Measurements were carried out at a steady flow rig, and discharge and flow coefficients were used to characterise the global engine breathability.

The global analysis has revealed the significant influence of the valve lift on the fluid dynamic efficiency of the intake and exhaust system. Different flow regimes have been registered, and flow separation phenomena at the valve head and seat have been observed at high valve lifts, in line with the literature results.

Furthermore, the investigation has shown the large effect produced by the throttle angle on the engine volumetric efficiency. A progressive increase in the head permeability was observed with the throttle angle opening. However, this effect became negligible when the throttle opening was larger than 70°. Moreover, the experimental characterisation has put in evidence that the transition phenomena from a flow condition to another one is reached at lower valve lifts when the flow is throttled.

Finally, the global analysis has demonstrated that a unique trend in the fluid dynamic efficiency of the intake system exists if an opportune dimensionless plot is adopted.