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Laser induced fluorescence (LIF) imaging during the expansion stroke, exhaust gas emissions, and cylinder pressure measurements were used to investigate the influence on combustion and CO/UHC emissions of variations in squish height and fuel spray targeting on the piston. The engine was operated in a highly dilute, partially premixed, low-temperature combustion mode. A small squish height and spray targeting low on the piston gave the lowest exhaust emissions and most rapid heat release. The LIF data show that both the near-nozzle region and the squish volume are important sources of UHC emissions, while CO is dominated by the squish region and is more abundant near the piston top. Emissions from the squish volume originate primarily from overly lean mixture. At the 3 bar load investigated, CO and UHC levels in mixture leaving the bowl and ring-land crevice are low.

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.

Homogeneous Charge Compression Ignition (HCCI) combustion is limited in maximum load due to high peak pressures and excessive combustion rate. If the rate of combustion can be decreased the load range can be extended. From previous studies it has been shown that by using a deep square bowl in piston geometry the load range can be extended due to decreased heat release rates, pressure rise rates and longer combustion duration compared to a disc shaped combustion chamber. The explanation for the slower combustion was found in the turbulent flow field in the early stages of the intake stroke causing temperature stratifications throughout the charge. With larger temperature differences the combustion will be longer compared to a perfectly mixed charge with less temperature variations. The methods used for finding this explanation were high-speed cycle-resolved chemiluminescence imaging and fuel tracer planar laser induced fluorescence (PLIF), together with large eddy simulations (LES).