Hydrogen as a Combustion Modifier of Ethanol in Compression Ignition Engines 2009-01-2814
Ethanol, used widely as a spark-ignition (SI) engine fuel, has seen minimal success as a compression ignition (CI) engine fuel. The lack of success of ethanol in CI engines is mainly due to ethanol's very low cetane number and its poor lubricity properties. Past researchers have utilized nearly pure ethanol in a CI engine by either increasing the compression ratio which requires extensive engine modification and/or using an expensive ignition improver.
The objective of this work was to demonstrate the ability of a hydrogen port fuel injection (PFI) system to facilitate the combustion of ethanol in a CI engine. Non-denatured anhydrous ethanol, mixed with a lubricity additive, was used in a variable compression ratio CI engine. Testing was conducted by varying the amount of bottled hydrogen gas injected into the intake manifold via a PFI system. The hydrogen flowrates were varied from 0 - 10 slpm. The engine was operated at compression ratios varying from 19:1 to 24:1 and intake air temperatures ranging from 80°C to 120°C.
To prevent injection system lubrication failure, castor oil and lauric acid were tested in various blends with ethanol according to ASTM D975. It was found that 2% by volume of lauric acid provided a wear scar diameter of 200 μm, very close to the diesel fuel wear scar diameter of 195 μm at 25°C, and was chosen as the lubricity additive.
Small amounts of hydrogen enabled ethanol operation at a compression ratio of 19:1 and an intake temperature of 80°C. This was a condition that was not sustainable without hydrogen injection. Adding hydrogen with the intake air advanced the start of combustion (SOC) timing for many of the conditions tested. The relatively small amounts of hydrogen necessary could be provided by an onboard ethanol reformer. Further work is necessary to determine why the hydrogen injection causes this SOC advance.