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This paper presents large eddy simulation (LES) and experimental studies of the combustion process of ethanol/air mixture in an experimental optical HCCI engine. The fuel is injected to the intake port manifolds to generate uniform fuel/air mixture in the cylinder. Two different piston shapes, one with a flat disc and one with a square bowl, were employed to generate different in-cylinder turbulence and temperature field prior to auto-ignition. The aim of this study was to scrutinize the effect of in-cylinder turbulence on the temperature field and on the combustion process. The fuel tracer, acetone, is measured using laser induced fluorescence (LIF) to characterize the reaction fronts, and chemiluminescence images were recorded using a high speed camera, with a 0.25 crank angle degree resolution, to further illustrate the combustion process. Pressure in the cylinder is recorded in the experiments.

It has been known from multi-zone simulations that HCCI combustion can be significantly affected by temperature stratification of the in-cylinder gas. With the same combustion timing (i.e. crank angles at 50% heat release, denoted as CA50), large temperature stratification tends to prolong the combustion duration and lower down the in-cylinder pressure-rise-rate. With low pressure-rise-rate HCCI engines can be operated at high load, therefore it is of practical importance to look into more details about how temperature stratification affects the auto-ignition process. It has been realized that multi-zone simulations can not account for the effects of spatial structures of the stratified temperature field, i.e. how the size of the hot and cold spots in the temperature field could affect the auto-ignition process. This question is investigated in the present work by large eddy simulation (LES) method which is capable of resolving the in-cylinder turbulence field in space and time.

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.

A five-cylinder diesel engine, converted to a single cylinder operated optical engine is run in Homogeneous Charge Compression Ignition (HCCI) mode. A blend of iso-octane and n-heptane is used as fuel. An experimental study of the horizontal boundary layer between the main combustion and the non-reacting surface of the combustion chamber is conducted as a function of speed, load, swirl and injection strategy. The combustion behaviour is monitored by chemiluminescence measurements. For all cases an interval from -10 to 16 crank angles after top dead center (CAD ATDC) in steps of one CAD are studied. One image-intensified camera observes the boundary layer up close from the side through a quartz cylinder liner while a second camera has a more global view from below to see more large scale structure of the combustion. The averaged chemiluminescence intensity from the HCCI combustion is seen to scale well with the rate of heat release.

Hydrogen has been proposed as a possible fuel for automotive applications. Methanol is one of the most efficient ways to store and handle hydrogen. By catalytic reformation it is possible to convert methanol into hydrogen and carbon monoxide. This paper reports an experimental investigation of Reformed Methanol Gas as Homogeneous Charge Compression Ignition (HCCI) engine fuel. The aim of the experimental study is to investigate the possibility to run an HCCI engine on a mixture of hydrogen and carbon monoxide, to study the combustion phasing, the efficiency and the formation of emissions. Reformed Methanol Gas (RMG) was found to be a possible fuel for an HCCI engine. The heat release rate was lower than with pure hydrogen but still high compared to other fuels. The interval of possible start of combustion crank angles was found to be narrow but wider than for hydrogen. The high rate of heat release limited the operating range to lean (λ>3) cases as with hydrogen.

A naturally aspirated in-line six-cylinder 2.9-litre Volvo engine is operated in Homogeneous Charge Compression Ignition (HCCI) mode, using camshafts with low lift and short duration generating negative valve overlap. Standard port fuel injection is used and pistons and cylinder head are unchanged from the automotive application. HCCI through negative valve overlap is recognized as one of the possible implementation strategies of HCCI closest to production. It is important to gain knowledge of the constraints and limits on the possible operating region. In this work, the emphasis is on investigating how cycle-to-cycle and cylinder-to-cylinder deviations limit the operating region, how these effects change in different parts of the operating region and how they can be controlled. At low load the cycle-to-cycle phenomena cause periodic behavior in combustion timing; together with cylinder deviations this is found responsible for decreasing the operating regime.

HCCI (Homogeneous Charge Compression Ignition), laser-assisted HCCI and spark plug-assisted HCCI combustion was studied experimentally in a modified single cylinder truck-size Scania D12 engine equipped with a quartz liner and quartz piston crown for optical access. The aim of this study was to find out how and to what extent the spark, generated to influence or even trigger the onset of ignition, influences the auto-ignition process or whether primarily normal compression-induced ignition remains prevailing. The beam of a Q-switched Nd:YAG laser (5 ns pulse duration, 25 mJ pulse energy) was focused into the centre of the cylinder to generate a plasma. For comparison, a conventional spark plug located centrally in the cylinder head was alternatively used to obtain sparks at a comparable location. No clear difference in the heat releases during combustion between the three different cases of ignition start could be seen for the fuel of 80/20 iso-octane/n-heptane used.

Hydrogen has been proposed as a possible fuel for automotive applications. This paper reports an experimental investigation of hydrogen as HCCI engine fuel. The aim of the experimental study is to investigate the possibility to run an HCCI engine on an extremely fast burning fuel such as hydrogen as well as to study the efficiency, the combustion phasing and the formation of emissions. The experiments were conducted on a single-cylinder research engine with a displacement volume of 1.6 litres and pancake combustion chamber geometry. Variation of lambda, engine speed, compression ratio and intake temperature were parts of the experimental setting. The engine was operated in Homogenous Charge Compression Ignition (HCCI) mode and as comparison also in Spark Ignition (SI) mode. Hydrogen was found to be a possible fuel for an HCCI engine. The heat release rate was extremely high and the interval of possible start of combustion crank angles was found to be narrow.

Recent experiments and numerical studies have showed that piston geometry has a significant effect on the homogeneous charge compression ignition (HCCI) process. There are two effects generated by the combustor geometry: the geometry affects the flow/turbulence in the cylinder; the geometry also affects the temperature stratification. The temperature stratification is more directly responsible for the observed alteration of the auto-ignition process. To clarify this issue further we present in this paper a study of two engines with the same geometry but difference ways of cooling. Measurement of the two engines - a metal engine and quartz piston engine, both with the same piston bowl geometry - is carried out. Large eddy simulation (LES) is used to simulate the flow, the temperature field and the auto-ignition process in the two engines. The fuel is ethanol with a relative air/fuel ratio of 3.3.