Guillaume Brecq

A new indicator for knock detection in gas SI engines

Determination of knock onset for any engine tuning remains a difficult work for many engine manufacturers. This study investigates different combinations of existing knock indices in order to produce an upgraded indicator, which is easier to calibrate. Experiments are conducted on a single-cylinder gas engine bounded to combined heat and power (CHP). Effects of spark advance, volumetric efficiency and equivalent ratio are studied under constant speed operation. The ratio IMPO/(MAPO×W) (with IMPO defined as the Integral of Modulus of Pressure Oscillations, MAPO as the Maximum Amplitude of Pressure Oscillations and W as the width of the computational window) is proposed as suitable indice. In any engine setting, it remains constant under no knocking conditions. When knock occurs, a model deduced from dimensionless analysis allows determination of the oversteps of Knock Limited Spark Advance from a single IMPO/(MAPO×W) measurement with an accuracy better than 1 CA. Knock is then studied for different gas qualities by adding propane or carbon dioxide to the fuel. The results show that there is no significant effect of the fuel composition on the proposed indicator, making the model able to calculate KLSA overstep in all the situations.

Knock rating of gaseous fuels in a single cylinder spark ignition engine

Abstract This paper presents the determination of knock rating of gaseous fuels in a single cylinder engine. The first part of the work deals with an application of a standard method for the knock rating of gaseous fuels. The Service Methane Number (SMN) is compared with the standard Methane Number (MN) calculated from the standard AVL software METHANE (which corresponds to the MN measured on a Cooperative Fuel Research engine). Then, in the second part, the ‘mechanical’ resistance to knock of our engine is highlighted by means of the Methane Number Requirement (MNR). A single cylinder LISTER PETTER engine was modified to run as a spark ignition engine with a fixed compression ratio and an adjustable spark advance. Effects of engine settings on the MNR are deduced from experimental data and compared extensively with previous studies. Using the above, it is then possible to adapt the engine settings for optimal knock control and performances. The error on the SMN and MNR stands beneath ±2 MN units over the gases and engine settings considered.

Modeling of In-cylinder Pressure Oscillations under Knocking Conditions: Introduction to Pressure Envelope Curve

High frequency pressure oscillations are generated under knocking conditions within the combustion chamber of Spark Ignition engines. Although acousticoscillation model can give the natural frequencies of these oscillations, very few mathematical models are today available, in scientific literature, to describe the oscillation deadening effect. An analytical formulation of the deadening has been highlighted. Analytical solution has been established for future ECU implementation. Coupling this new concept and an existing highfrequency model, an achieved model of the knocking pressure high frequencies is compared to experimental data. Good behavior is obtained on a natural gas fuelled spark ignition engine. BACKGROUND Knock is an undesirable combustion mode occurring in SI engines. It results in an abnormal auto-ignition of the end gas ahead of the propagating flame front. This phenomenon, characterized by the occurrence of pressure oscillations within the combustion chamber resulting in a metallic noise, can lead to irreversible engine damage. Because of increasing environmental concerns and enlargement of fuel diversification, natural gas is more and more considered as a valuable fuel for reciprocating engines and especially SI engines. Because of the absence of anti-knock-additive for natural gas (such as lead tetraethyl for gasoline) and the relative high variability of the natural gas composition (natural gas is a crude hydrocarbon whose composition changes with feedstock location), knocking conditions can easily occur in gas engines. Consequently, although this phenomenon has been extensively studied for more than

Knock prevention of CHP engines by addition of N2 and CO2 to the natural gas fuel

This work focuses on the prevention of knock in the case of spark ignition (SI) engines supplied by natural gas network. The effects of the addition of two inert gases (N2 and CO2) are experimentally studied. The added volumetric quantities are between 0% and 25% for N2 and between 0% and 15% for CO2. The thermal efficiency and the emissions of the engine are very slightly affected by the addition, whereas a significant increase of the knock limited spark timing (KLST) is always measured. A twice-higher augmentation of KLST is noted when CO2 is added compared to N2 for an equivalent volumetric concentration. The overall augmentation varies between +1 and +6 °CA depending on engine operation. Finally, a law for predicting the KLST augmentation implied by the addition of inert gases is deduced from all the measurements.

Thermoeconomic analysis based on energy structure for combined heat and power

This paper proposes a unified comparison method for the calculations of thermodynamic efficiencies applied to combined heat and power (CHP) plants. Two new dimensionless indices are introduced. They are used to estimate the influence of technical and economical features on the profitability of a CHP plant. A case of a CHP installation by internal combustion engine is treated as a practical application.

Knock Prevention of Gas SI Engine by Adjunction of Inert Gases to the Fuel

This work focuses on the prevention from knock in the case of SI engines supplied by natural gas network. The effect of two inert gases (N2 and CO2 ) adjunction is experimentally studied. The added quantities are between 0% and 25% in volume for N2 and between 0% and 15% for CO2 . A significant increase of the Knock Limited Spark Timing (KLST) is measured in all the cases. A twice-higher augmentation is noted when CO2 is added compared to N2 for an equivalent volumetric concentration. The overall augmentation varies between +1 to +6 °CA depending on the operation. Finally, a law for predicting the KLST augmentation implied by the adjunction of inert gases is deduced from all the measurements.© 2002 ASME

Service Methane Number as a Means to Avoid Knock in Natural Gas Fuelled Spark Ignition Engines

Experimental investigations on the knock rating of gaseous fuels were carried out on a single cylinder SI engine of Lister-Petter make. The Service Methane Number (SMN) of different gas compositions is measured and then compared to the standard Methane Number (MN), calculated by the AVL software. Effects of engine parameters, by mean of the Methane Number Requirement (MNR) are also highlighted. A linear correlation, between the SMN and the MN, has been obtained with a maximum absolute deviation lower than 2 MN units. A prediction correlation giving the MNR from engine parameters has finally been deduced from experimental data with a good accuracy (mean absolute deviation of 0.5 MNR unit).© 2003 ASME