Impact of H2-NG blending on performance and emissions of stoichiometric and lean burn spark ignited engines

Abstract

The energy crisis and growing environmental concerns are serious problems faced all over the world today. Renewable sources like solar and wind energy are often perceived to be the solution but high market penetration utilizing these sources directly has limitations. These sources cannot be relied upon for base load and the demand-supply mismatch makes them impractical for peaking applications. To address this, energy storage mechanisms like chemical storage can be employed to smooth the available renewable energy supply over time. More specifically, electrolysis of water can be carried out to create hydrogen, utilizing the electricity produced from solar and wind. This hydrogen may then be blended with natural gas in pipelines to be used in natural gas applications. Blending hydrogen with natural gas (H2-NG blend) significantly changes properties of the gas. The goal of this project is to study the impact of H2-NG blend on spark-ignited internal combustion engines. To evaluate the impact of H2-NG blend on stoichiometric engine performance, testing was performed on a 7.5 L Cummins Onan Generator Set, model GGHD 60Hz, equipped with an NSCR catalyst. Two different carburetor/lambda sensor combinations were tested with the NSCR catalyst to assess impact of blending different percentages of hydrogen into natural gas on catalyst efficiency as well as engine performance and emissions. Criteria for emissions considered for this testing was South Coast Air Quality Management District Rule 1110.2 limits of 11 ppmd NOx, 250 ppmd CO and 30 ppmd VOCs, corrected to 15% oxygen. Stoichiometric testing was also performed on a Cooperative Fuel Research (CFR) engine to perform combustion analysis. The CFR is an F-2 model manufactured by Waukesha Engine, Dresser Industries. It is a single cylinder, 4-stroke, spark-ignited engine with a constant speed of 940 rpm, which can be operated at various compression ratios from 4:1 to 18:1. An in-cylinder pressure transducer (Kistler model 6061A) was installed for recording detailed in-cylinder pressure data, which was used to analyze engine knock. Base fuel for the engine was a blend of 90% methane (CH4) and 10% ethane (C2H6). The engine was tested at various H2-NG blends to assess impact of H2 on engine knock and determine critical compression ratio at each blend, as well as determine impact on ignition delay and combustion rate. Testing was also performed on the CFR engine to evaluate impact of hydrogen on lean burn operation. Increasing percentages of H2 were added to the base fuel to study the effect on emissions as well as lean burn limit of engine operation. Results showed that NOx emissions tend to increase with hydrogen addition, while THC and CO emissions show marked reduction. Up to 10% hydrogen may be added to natural gas; the exact value depends on particular engine configuration and emission norms. Also, adding hydrogen increases engine susceptibility to knock at stoichiometric operation, and improves combustion at lean operation, allowing the engine to operate at leaner equivalence ratios. Operating at lean limit with retarded spark ignition timing to offset faster flame speeds of hydrogen can help reduce NOx emissions considerably.