Research conducted at the Supercritical (SC) facility of MIT's Energy Laboratory provided visual confirmation of a single phase, homogeneous water/fuel mixture near the critical temperature and pressure of water. Equal volumes of water and diesel fuel were observed to be completely miscible, and high temperature polymerization of fuel molecules was not found. This is believed to be the first observation of a solution of diesel fuel and water.
This mixture was subsequently burned under atmospheric spray conditions with very low NOx, smoke, CO, and HC. The results suggested that in-cylinder combustion in a compression ignition engine was warranted.
Tests were conducted in a single cylinder, air-cooled, naturally aspirated, 3.5 horsepower Yanmar diesel engine. The compressibility of this new fuel composition necessitated a modified injector to provide smooth operation. An electronically controlled, common rail injection system was developed using modified injectors to operate at temperatures above 350°C in the presence of water.
Early results comparing injection and combustion of this fuel/water solution with standard diesel operation were uniformly positive. An 85% decrease in NOx and a virtual elimination of smoke was measured on an AVL smoke meter. Noise levels were reduced by 2.7dB. Efforts are continuing with larger engines and injection optimization.