Hydrogen Fuel
Hydrogen has a high specific energy, high flame speed, wide range of flammability, and clean burning characteristics which suggest a possibility of high performance in internal combustion engines (ICE). These attributes have been realized for more than half a century since the onset of hydrogen engine development. In the early 1990s, FSEC conducted research on using hydrogen in an ICE. This work resulted in the development of a mixed fuel called HYTEST. Today, automobile manufacturers and DOE continue to work on hydrogen-powered ICEs. | Hydrogen/natural gas fueling (HYTEST fuel) of Ford Ranger, FSEC H2 Lab
(Photo: S. Spencer) |
There are four basic issues regarding hydrogen-fueled engines and vehicles: engine backfire and susceptibility of hydrogen to surface ignition, somewhat reduced engine power, high nitric oxide (NOx) emissions, and the problem of on-board storage of the fuel and safety. Although partial solutions have been found to most of these problems, there still is no general consensus of the best method to finally resolve all of these issues.
As far as the performance of a hydrogen engine is concerned, its limit of flammability in air is the most important factor. Hydrogen's low lean limit of flammability provides an opportunity to use the lean-burn engine (LBE) concept with hydrogen engines quite successfully. The LBE concept refers to engine operation that is leaner (higher air to fuel mass ratio) than stoichiometric (chemically correct air-fuel ratio). The amount of work done during the expansion process in a lean-burn engine is relatively large (due to lower cycle temperature), resulting in a proportionally higher thermal efficiency.
The LBE concept with hydrogen further facilitates and promotes the use of so-called "mixture regulation" or "quality governing" at light engine loads. Unlike gasoline-fueled engines that require throttling at lower engine loads, hydrogen-fueled engines can be operated at reduced power levels by limiting only
(Photo: S. Spencer) |
There are four basic issues regarding hydrogen-fueled engines and vehicles: engine backfire and susceptibility of hydrogen to surface ignition, somewhat reduced engine power, high nitric oxide (NOx) emissions, and the problem of on-board storage of the fuel and safety. Although partial solutions have been found to most of these problems, there still is no general consensus of the best method to finally resolve all of these issues.
As far as the performance of a hydrogen engine is concerned, its limit of flammability in air is the most important factor. Hydrogen's low lean limit of flammability provides an opportunity to use the lean-burn engine (LBE) concept with hydrogen engines quite successfully. The LBE concept refers to engine operation that is leaner (higher air to fuel mass ratio) than stoichiometric (chemically correct air-fuel ratio). The amount of work done during the expansion process in a lean-burn engine is relatively large (due to lower cycle temperature), resulting in a proportionally higher thermal efficiency.
The LBE concept with hydrogen further facilitates and promotes the use of so-called "mixture regulation" or "quality governing" at light engine loads. Unlike gasoline-fueled engines that require throttling at lower engine loads, hydrogen-fueled engines can be operated at reduced power levels by limiting only