Client
Hythane
Project Objectives
- Measure the additional displacement of diesel fuel that can be achieved with the blending of hydrogen in a natural gas dual-fuel diesel engine
- Quantify the overall fuel cost savings that is achieved with hydrogen enrichment as a function of engine load (include cost of hydrogen generation and storage)
- Measure the emissions reduction that is achieved with hydrogen enrichment as a function of engine load
Summary of Project and Results (Non-Confidential)
Project Introduction
The difference in cost between natural gas and diesel fuel has been increasing and that trend is expected to continue in the long term. The diesel vehicle transportation industry is looking for ways to reduce fuel costs. A natural gas-diesel dual-fuel engine is a proven technology that can provide substantial fuel savings. Expensive diesel fuel is substituted with natural gas, and only a small amount of diesel is used to ignite the natural gas-air mixture. A relatively simple and inexpensive retrofit kit is used to convert the diesel engine into a natural gas dual-fuel engine. The natural gas fuel is stored on-board the vehicle by compressing it to high pressure, or cryogenically cooling it, or a combination of both, to provide adequate storage density.
A variety of studies have shown that natural gas dual-fuel engines provide dramatic reductions in NOx and particulate emissions. Natural gas also produces substantially less CO2 compared to diesel combustion, which could be important in meeting future global warming restrictions. One issue with natural gas dual-fuel engines is that some tests have shown relatively high emissions when the engines are operating at light-loads. This is because the low concentration of natural gas has approached the lean limit and some of the natural gas has remained unburned.
It was thought that the blending of hydrogen with natural gas (Hythane®)* in a dual-fuel diesel engine could provide a significant reduction in diesel fuel cost and generation of emissions. At light loads, hydrogen extends the lean combustion limit of natural gas in air. At heavy loads, hydrogen extends the knock-limited proportion of diesel fuel displacement by natural gas. A significant benefit of hydrogen enrichment is that it could remedy the poor performance of dual-fuel engines at low-loads.
*Hythane is a Registered Trademark of Hythane Co.
Project Description
A standard heavy-duty diesel engine was converted to run as a duel-fuel engine with a blend of hydrogen and natural gas. This process involved modifying the air intake line to allow the injection of natural gas and hydrogen. The second step was to modify the control of the diesel fuel injection pump.
A series of tests were run to obtain baseline fuel consumption and emissions data for the original diesel engine.
A second series of tests were run to determine the baseline operation of the dual-fuel engine operating on natural gas and diesel fuel. The tests examined the amount of displacement of diesel fuel with natural gas that provides the required engine power over a range of engine loads, and prevented the occurrence of knocking. The engine emissions were measured at all operating conditions, including light loads where hydrocarbon emissions were expected to be high.
A third series of tests were run with hydrogen injected with natural gas in a homogeneous mixture. The tests determined the maximum amount of diesel fuel that was displaced with hydrogen enrichment; provided the required engine power and prevented knocking, over a range of engine loads. Engine emissions were measured at all conditions, including light loads where hydrogen enrichment was expected to be effective in reducing hydrocarbon emissions.
A cost analysis was performed to determine the overall fuel cost savings that was provided with hydrogen enrichment. The cost of hydrogen generation, fuel station storage, dispensing, and on-board storage was included in the analysis so that the fuel cost savings represented a true savings.
Results
The tests found a substantial reduction in overall fuel costs with hydrogen enrichment. The fuel cost reduction includes the cost of hydrogen generation. NOx and CO2 emissions also decreased by a large amount. The fuel cost and emissions reduction were found over a range of engine loads. A dramatic reduction in emissions at low-loads was found when operating with hydrogen enrichment.
The hydrogen that would be used to blend with natural gas in a dual-fuel vehicle would be generated by the auto-thermal reforming of natural gas. Hydrogen would be stored on-board the vehicle separate from the natural gas. New Vista Research has developed a compressed-cryogenic hydrogen storage technology that provides a cost-effective method for high density on-board hydrogen storage. The project has shown that the economic benefits of hydrogen enrichment outweigh the costs of hydrogen generation and storage in hydrogen blended natural gas dual-fuel engines.
Future work will involve the separate injection of propane and hydrogen. This will allow the analysis of the effect of stratified hydrogen, which may improve performance more than a homogeneous mixture of hydrogen.