Aqueous fueled engines have the potential for lower emissions and higher engine efficiency than engines fueled with gasoline or diesel engines. Past attempts to burn aqueous fuels in over-the-road vehicles have been unsuccessful due to difficulties in initiating combustion under varying environmental conditions. Ethanol-water mixtures, called Aquanol, require no special emulsifications to create and should provide significant emission reductions in carbon monoxide (CO) and nitrous oxide (NOx,) while producing no net carbon dioxide (CO2) emissions. Aldehydes, a part of the hydrocarbon emissions, are expected to increase with alcohol-based fuels. Understanding the parameters that affect aldehyde formation will help create reduction strategies. Detailed detection of exhaust emissions is necessary for a quantitative comparison.
Redundant measurements with two special purpose detectors were used for emission comparisons. A van supplied by Valley Transit of Lewiston, Idaho was converted to catalytic ignition. Modifications to the fuel handling, engine management, and ignition system were necessary to make the vehicle operate on either gasoline or Aquanol. A three-part vehicle test plan is currently underway to compare performance, fuel economy, and emissions between Aquanol and gasoline fuels.
In the catalytically ignited ethanol-water system, ignition timing can be adjusted by changing the length of the catalytic core element, the length of the pre-chamber, the diameter of the pre-chamber, and the electrical power supplied to the catalytic core element.
A multi-zone energy balance model has been developed to understand ignition timing of ethanol-water mixtures. Model predictions agree with pressure versus crank angle data obtained from a 15 kW Yanmar diesel engine converted for catalytic operation on ethanol-water fuel. Comparing the converted Yanmar to the stock engine shows an increase in torque and power, with improvements in CO and NOx emissions. Hydrocarbon emissions increased significantly, but are largely due to piston geometry not well suited for homogeneous charge combustion. Future engine modifications have the potential to lower emissions to current emission standards, without requiring external emission control devices.
A catalytic plug flow reactor is being built to better understand the heterogeneous combustion of ethanol-water-air mixtures. A key figure is the reactor's ability to rapidly mix fuel vapor and air streams. A prototype mixing nozzle, designed and built last year, was evaluated using gas streams of two different compositions.
The chemical kinetic's code HCT (hydrodynamics, combustion and transport), developed by Lawrence Livermore National Laboratory, is being used to model gasphase combustion of ethanol-water-air mixtures. A literature search of surface reaction mechanisms was performed. HCT will be modified to accommodate surface reactions, and thus be available as a tool for better understanding of catalytic ignition of aqueous ethanol.