publication . Doctoral thesis . 2007

Modelling for Fuel Optimal Control of a Variable Compression Engine

Nilsson, Ylva;
Open Access English
  • Published: 01 Jan 2007
  • Publisher: Linköpings universitet, Institutionen för systemteknik
  • Country: Sweden
Abstract
Variable compression engines are a mean to meet the demand on lower fuel consumption. A high compression ratio results in high engine efficiency, but also increases the knock tendency. On conventional engines with fixed compression ratio, knock is avoided by retarding the ignition angle. The variable compression engine offers an extra dimension in knock control, since both ignition angle and compression ratio can be adjusted. The central question is thus for what combination of compression ratio and ignition angle the maximum efficiency is achieved, considering the set of compression ratios and ignition angles that give a sufficiently low knock intensity. Four k...
Subjects
arXiv: Nuclear Theory
free text keywords: combustion engine, modelling, Vehicle Engineering, Farkostteknik
Related Organizations
19 references, page 1 of 2

1 Control by compression ratio and ignition timing 1 1.1 Why fuel efficiency is important . . . . . . . . . . . . . . . . . . . 2 1.2 Knock in spark-ignited engines . . . . . . . . . . . . . . . . . . . 3 1.3 The variable compression engine . . . . . . . . . . . . . . . . . . 3 1.3.1 Other VCR engine concepts . . . . . . . . . . . . . . . . . 4 1.4 Fuel optimal control of a variable compression engine . . . . . . . 7 1.4.1 A closer look at the optimisation problem . . . . . . . . . 9 1.5 Limitations and assumptions . . . . . . . . . . . . . . . . . . . . 11 1.6 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.7 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2 Detection of knock and knock-onset 15 2.1 Engine knock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.1.1 Detonation theory . . . . . . . . . . . . . . . . . . . . . . 16 2.1.2 Auto-ignition theory . . . . . . . . . . . . . . . . . . . . . 17 2.1.3 Knock signature . . . . . . . . . . . . . . . . . . . . . . . 19 2.2 Knock detection methods and sensors . . . . . . . . . . . . . . . 20 2.3 Investigated knock detection methods . . . . . . . . . . . . . . . 21 2.3.1 Overview of the methods . . . . . . . . . . . . . . . . . . 21 2.3.2 Algorithm components . . . . . . . . . . . . . . . . . . . . 22 2.3.3 Off-line test quantity (OFF) . . . . . . . . . . . . . . . . . 24 2.3.4 On-line test quantity I (ONI) . . . . . . . . . . . . . . . . 25 2.3.5 On-line quantity II (ONII) . . . . . . . . . . . . . . . . . 26 2.3.6 On-line quantity III (ONIII) . . . . . . . . . . . . . . . . 27 2.3.7 Parameters of detection test quantities . . . . . . . . . . . 27 2.3.8 Thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.4 Pressure noise characteristic . . . . . . . . . . . . . . . . . . . . . 28

2.5 Evaluation on cylinder pressure . . . . . . . . . . . . . . . . . . . 29 2.5.1 Knowing the true knock on-set . . . . . . . . . . . . . . . 30 2.5.2 Detected knock and estimated knock angle . . . . . . . . 34 2.5.3 Robustness . . . . . . . . . . . . . . . . . . . . . . . . . . 37

2.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3 Correlation between knock intensity measures 43 3.1 Some notes about the correlation study . . . . . . . . . . . . . . 45 3.2 Knock intensity measures . . . . . . . . . . . . . . . . . . . . . . 46 3.2.1 Logarithmic normalised knock energy . . . . . . . . . . . 46 3.2.2 Unburned mass fraction at knock onset . . . . . . . . . . 49 3.3 Knock intensity and unburned fuel at knock onset . . . . . . . . 53 3.4 Knock intensity and rate of occurrence . . . . . . . . . . . . . . . 55 3.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

4 A new formulation of multi-zone combustion engine models 67 4.1 The multi-zone combustion model . . . . . . . . . . . . . . . . . 68 4.1.1 Existence of a solution and uniqueness . . . . . . . . . . . 71 4.2 Simulation aspects . . . . . . . . . . . . . . . . . . . . . . . . . . 71 4.2.1 Empty zones - Initialising a new zone . . . . . . . . . . . 72 4.2.2 Ill-conditioned A matrix-Adaptive scaling . . . . . . . . 73 4.2.3 Finite precision - Exclusion of zones . . . . . . . . . . . . 74 4.2.4 Accumulated faults - Consistency equations . . . . . . . . 74 4.3 Usage of model in other phases than the combustion phase . . . 75 4.4 Illustration of concept . . . . . . . . . . . . . . . . . . . . . . . . 75 4.4.1 Simulation set-up and initialisation . . . . . . . . . . . . . 76 4.4.2 Simulation results . . . . . . . . . . . . . . . . . . . . . . 77 4.5 Applications utilising the presented model . . . . . . . . . . . . . 80 4.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

5 Torque model for a variable compression engine 83 5.1 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 5.1.1 Torque contours . . . . . . . . . . . . . . . . . . . . . . . 85 5.1.2 Knock intensity . . . . . . . . . . . . . . . . . . . . . . . . 87 5.2 Engine torque model . . . . . . . . . . . . . . . . . . . . . . . . . 87 5.2.1 Pumping losses . . . . . . . . . . . . . . . . . . . . . . . . 88

65 5.2.2 Gross indicated work . . . . . . . . . . . . . . . . . . . . . 92

5.3 Validation of the model for indicated work . . . . . . . . . . . . . 94 5.3.1 Optimal compression ratio and ignition angle . . . . . . . 97

5.4 Friction losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

5.5 Validation of the torque model . . . . . . . . . . . . . . . . . . . 102 5.5.1 Optimal compression ratio and ignition angle . . . . . . . 103

5.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

A The geometry of the SVC engine 111 A.1 Engine geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 A.2 Cylinder volume . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 A.3 Volume function comparisons . . . . . . . . . . . . . . . . . . . . 115 A.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

B Engine measurements 119 B.1 Data sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 B.2 Crank angle and cylinder pressure . . . . . . . . . . . . . . . . . 124

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