This study investigates the combustion and emissions of a
compression ignition (CI) engine operating with mixtures of
hydrogen (H₂) and carbon monoxide (CO) injected with the intake
air. Hydrogen and carbon monoxide were chosen as the gaseous fuels,
because they represent the main fuel component of synthesis gas,
which can be produced by a variety of methods and feed stocks.
However, due to varying feed stock and production mechanisms,
syngas composition can vary significantly. It is currently unknown
how a varying H₂/CO (syngas) ratio affects the cycle efficiency and
gaseous emissions. The experiments were performed on an air-cooled,
naturally aspirated, direct injection diesel engine. The engine was
operated at 1800 RPM with a compression ratio of 21.2:1. Two load
conditions were tested; 2 bar and 4 bar net indicated mean
effective pressure (IMEPⁿ).
For all test conditions the added syngas demonstrated lower
cycle efficiency than the diesel fuel baseline. The lower cycle
efficiency is thought to directly come from the amount of unburned
syngas escaping with the exhaust gases. For the 2 bar IMEPn
condition the NOx emissions remained relatively constant
for all conditions tested, however for the 4 bar IMEPⁿ condition,
the NOx emissions increased with diesel fuel
substitution for all H₂/CO proportions. The NO₂/NOx
ratio was found to significantly increase for all conditions
tested, compared to the diesel base case. It is speculated that
this increase is caused by the increase in HO₂ radicals which
increases the NO to NO₂ conversion.