Troels Dyhr Pedersen.indd - Solid Mechanics

RPM with EGR, the combustion appears to be incomplete before EGR is applied. Apart from these two cases,
all EGR experiments resulted in low CO levels.
Using methanol at 1800 RPM seemed to cause high levels of CO regardless of engine load. The reason for this
effect is unknown.
The DOC effectively converts CO when the exhaust gas temperature is above 200° C. Since the DOC will
usually be hotter than this, the emission of CO is believed to be reduced permanently and is thus of minor
importance to the impact on air quality.
CONCLUSION
It has been demonstrated that a diesel engine with a compression ratio of 14.5 and a DI common rail system is
suitable for dual fuel HCCI combustion. DME was injected directly through the common rail injectors and the
methanol was port injected. The effect of high quantities of EGR was also demonstrated.
Combustion timing control was first demonstrated with methanol. The best result was achieved when the
equivalence ratio of methanol reached 0.120 at 1000 RPM and 0.076 at 1800 RPM. These quantities ensured
complete combustion about 5 CAD ATDC at the respective engine speeds. Increasing the quantity further
caused partial combustion and misfire at both engine speeds.
A BMEP of 440 kPa was achieved at 1000 RPM and 380 kPa was reached at 1800 RPM with the optimum
quantity of methanol. The corresponding brake efficiencies were 0.35 and 0.31 respectively, which is close to
the performance of the original engine.
Methanol proved to reduce engine knock to a very low level despite the increased equivalence ratio. It may
therefore be used to increase the engine power by enabling higher equivalence ratios.
A disadvantage of the port injection was that a large quantity of the injected methanol was diluted into the
lubrication oil. This problem could possibly be avoided by mixing the methanol with the DME at a fixed ratio
and injecting the mixture as a whole through the common rail injectors.
EGR was also used to retard combustion timing for a fixed quantity of DME. For EGR percentages up to 65, the
delay in CAD was proportional to the EGR percentage. At an EGR percentage of 70 % the rate of reaction was
reduced and the heat release appeared around 2-3 CAD BTDC.
BMEP increased with increasing amounts of EGR due decreased heat losses and less compression work. The
highest BMEP obtained was around 260 kPa at both 1000 and 1800 RPM.
Engine knock was virtually eliminated when the EGR level increased the equivalence ratio close to 1, as the
rate of reaction was lowered.
Combustion control of DME HCCI through simultaneous use of methanol and EGR may possibly enable the
use of even higher compression ratios than 14.5. This could allow for standard diesel engines to utilize the
HCCI combustion process in part load situations.
In general, NOx emissions were in the 0-30 ppm range. At the operating points with the best thermal
efficiencies, the calculated specific emissions of NOx were close to or less 0.1 g/kWh.
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