Experimental investigation of the effect of engine settings on the wall heat flux during HCCI combustion

Abstract

Homogeneous charge compression ignition (HCCI) engines are a promising alternative to traditional spark-and compression-ignition engines, due to their potential to achieve a high thermal efficiency and near-zero emissions of NO x and soot. In this work, the heat transfer from the bulk gas to the cylinder wall is measured during motored and HCCI operation in a single cylinder (CFR) engine fueled with n-heptane. Heat flux measurements in the cylinder wall and head show small spatial variation of the heat flux in the combustion chamber. Design of Experiments methods are applied to study the effect of the engine settings on the heat transfer. It is found that the inlet air temperature does not affect the heat flux under motored operation. Under fired operation, all engine settings affect the heat transfer, but none of their interactions are significant. The compression ratio and inlet air temperature have a quadratic effect on the peak heat flux and peak convection coefficient, whereas the mass fuel rate has a linear effect. For the total heat released, the compression ratio and inlet air temperature have a linear effect and the mass fuel rate has a quadratic effect on it. All engine settings affect the instantaneous heat flux.

Evaluation of Wall Heat Flux Models for Full Cycle CFD Simulation of Internal Combustion Engines under Motoring Operation

“…Three other sensor locations are situated in the liner, with the center of the sensor 9 mm below the cylinder head and evenly spaced around the cylinder bore. These probes are Vatell HFM-7 sensors, which consist of a thermopile, capable of determining the heat flux, and a Resistance Temperature Detector or RTD to measure the wall temperature [4]. A Vatell AMP-6 amplifier is used to amplify the electrical output signals, which are directly correlated to the measured quantities through the calibration constants supplied by the manufacturer [4].…”

“…They however all have a general appearance, namely a linear and a logarithmic part, which resembles the momentum wall model given in Equation 2. An example of such a thermal law of the wall is the most simple model, derived by Launder and Spalding [20]: (4) where A + is the van Driest constant which has a value of 26 and T + is the non-dimensional temperature, derived by subtracting the wall temperature T w from the temperature T and dividing by the shear temperature T τ . Together with the relationship between T τ and the wall heat flux q w , this heat flux can be calculated.…”

“…Heat transfer calculations play an important part in the optimizing strategy of internal combustion engines, as it influences the engine efficiency, power output and emissions [1,2,3,4,5,6,7,8]. Currently, research is focused on two aspects: simulation strategies on the one hand, to predict the heat flux in an accurate manner and aid in reducing the time-consuming approach of only relying on experiments; and on the other hand, developing new measurements tools to accurately capture the heat flux and other experimental parameters, as an aid for optimization as well as validation of these simulation strategies.…”

Evaluation of wall heat flux calculation methods for CFD simulations of an internal combustion engine under both motored and HCCI operation

“…There are a number of problems here. First, only recently have experimental data using more advanced measurements techniques become available for the new combustion modes currently being studied [9]. Thus, modeling approaches for these modes have not yet been validated.…”

“…A possible solution is the development and use of Thin Film Gauge sensors as described by Thorpe et al [11] and De Cuyper et al [12,13]. Their applicability for engine research has been shown by Broekaert et al [9,14] by measuring the heat flux in a HCCI operated research engine as well as in a production type engine operating in PPC mode [15]. De Cuyper et al [16] also demonstrated their use to measure the heat flux in a production type spark ignition engine.…”