This report is about the process of converting a petrol-fuelled Honda GX35 engine to run
on methane gas. The future goal is to use the engine in the engineering competition Shell
Eco-marathon, where the aim is to drive a vehicle as far as possible with a set amount of
fuel.
To enable methane fuelling, the carburator of the GX35 was replaced with a gas fuel injector
from the engine accessory company Ecotrons. This was attached to an aluminium intake pipe
constructed by the project group. A new flywheel was constructed, equipped with twelve
magnetic detection points instead of one for more accurate detection of the crankshaft
position. A magnet was also attached to the upper cam pulley to enable position detection.
The original exhaust system was replaced by a holder of a lambda sensor and a straight
exhaust pipe. Together with the engine control unit (ECU) KATLA, developed earlier for a
bachelor’s thesis at Chalmers, this enabled detailed control of ignition and fuel injection, as
well as measurement of the air-fuel ratio.
In order to test the engine with a load, a brake device was constructed. A moped was
acquired, whose gearbox and rear brake was used to brake and gear down the output shaft
of the methane engine. The flywheel of the methane engine was connected to the flywheel of
the moped through a vibration reducing rubber disc and a steel adapter. The rear wheel of
the moped was lifted from the ground with a support so that it could rotate freely. By doing
this, the load of the engine could be controlled with the rear brake pedal of the moped.
Methane was not available for the project group, so the engine was tested with liquefied
petroleum gas instead, which is another gaseous fuel. Before the engine was started, the flow
rate through the gas injector was measured. This data was used to set the fuel parameters
in the ECU. With some minor adjustments the engine ran well during testing.