The Effect of Hydrogen Enrichment on EGR Tolerance in Spark Ignited Engines 2007-01-0475

Small (up to 1% by volume) amounts of hydrogen (H₂) were added to the intake charge of a single-cylinder, stoichiometric spark ignited engine to determine the effect of H₂ addition on EGR tolerance. Two types of tests were performed at 1500 rpm, two loads (3.1 bar and 5.5 bar IMEP), two compression ratios (11:1 and 14:1) and with two fuels (gasoline and natural gas). The first test involved holding EGR level constant and increasing the H₂ concentration. The EGR level of the engine was increased until the CoV of IMEP was > 5% and then small amounts of hydrogen were added until the total was 1% by volume. The effect of increasing the amount of H₂ on engine stability was measured along with combustion parameters and engine emissions. The results showed that only a very small amount of H₂ was necessary to stabilize the engine. At amounts past that level, increasing the level of H₂ had no or only a very small effect.

The second test was to fix the H₂ level at 1% by volume and measure the EGR limit increase of the engine. At low load conditions, the EGR limit increased from the previous high of 25% to over 50% for gasoline and from 20% to 28% for CNG. At high load conditions, the EGR limit was achieved when the engine reached wide-open throttle and the addition of extra EGR would have required reducing the engine load. The results of this test indicate that the addition of even small amounts of H₂ can significantly improve the EGR tolerance of the engine when fueled with gasoline. This improvement in EGR tolerance can lead to reduced emissions and the potential to improve fuel economy by allowing high compression ratio operation. High IMEP was not tested with natural gas. Part load performance and EGR tolerance was explored to characterize the benefit hydrogen enriched EGR can provide to the emerging stoichiometric heavy duty natural gas engine community.