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The main benefit of HCCI engines compared to SI engines is improved fuel economy. The drawback is the diluted combustion with a substantially smaller operating range if not some kind of supercharging is used. The reasons for the higher brake efficiency in HCCI engines can be summarized in lower pumping losses and higher thermodynamic efficiency, due to higher compression ratio and higher ratio of specific heats if air is used as dilution. In the low load operating range, where HCCI today is mainly used, other parameters as friction losses, and cooling losses have a large impact on the achieved brake efficiency. To initiate the auto ignition of the in-cylinder charge a certain temperature and pressure have to be reached for a specific fuel. In an engine with high in-cylinder cooling losses the initial charge temperature before compression has to be higher than on an engine with less heat transfer.

Heavy trucks contribute significantly to the overall air pollution, especially NOx and PM emissions. Models to predict the emissions from heavy trucks in real world on road conditions are therefore of great interest. Most such models are based on data achieved from stationary measurements, i.e. engine maps. This type of “quasi stationary” models could also be of interest in other applications where emission models of low complexity are desired, such as engine control and simulation and control of exhaust aftertreatment systems. In this paper, results from quasi stationary calculations of fuel consumption, CO, HC, NOx and PM emissions are compared with time resolved measurements of the corresponding quantities. Measurement data from three Euro 3-class engines is used. The differences are discussed in terms of the conditions during transients and correction models for quasi stationary calculations are presented. Simply using engine maps without transient correction is not sufficient.

In-cylinder flow measurements, conventional swirl measurements and CFD-simulations have been performed and then compared. The engine studied is a single cylinder version of a Scania D12 that represents a modern heavy-duty truck size engine. Bowditch type optical access and flat piston is used. The cylinder head was also measured in a steady-flow impulse torque swirl meter. From the two-dimensional flow-field, which was measured in the interval from -200° ATDC to 65° ATDC at two different positions from the cylinder head, calculations of the vorticity, turbulence and swirl were made. A maximum in swirl occurs at about 50° before TDC while the maximum vorticity and turbulence occurs somewhat later during the compression stroke. The swirl centre is also seen moving around and it does not coincide with the geometrical centre of the cylinder. The simulated flow-field shows similar behaviour as that seen in the measurements.

The object of this paper is to present a new way of analyzing in-cylinder velocity measurements. The technique is called Discrete Wavelet Transform (DWT) and it is similar to Fast Fourier Transform (FFT) with one important difference it is possible to obtain both time localized and frequency resolved information. This paper demonstrates the use of DWT calculations on in-cylinder LDV flow measurements for different combustion geometries in a natural gas converted truck engine. It will furthermore provide some information about how DWT can be used with in-cylinder measurements in the future.

The most economical way to convert truck and bus DI-diesel engines to natural gas operation is to replace the injector with a spark plug and modify the combustion chamber in the piston crown for spark ignition operation. The modification of the piston crown should give a geometry well suited for spark ignition operation with the original swirling inlet port. Ten different geometries were tried on a converted VOLVO TD102 engine and a remarkably large difference in the rate of combustion was noted between the chambers. To find an explanation for this difference a cycle resolved measurement of the in-cylinder mean velocity and turbulence was performed with Laser Doppler Velocimetry (LDV). The results show a high correlation between in cylinder turbulence and rate of heat release in the main part of combustion.