Reduction of Cooling Loss in Hydrogen Combustion by Direct Injection Stratified Charge

Improving thermal efficiency by reducing cooling losses in hydrogen combustion engines

“…However this method also decreases the degree of constant volume and does not lead to effective thermal efficiency improvements. (4) A stratified charge by direct fuel injection into a lean mixture reduces the heat transfer from the burning gas to the combustion chamber walls and increases the apparent heat release fraction in hydrogen combustion. The cooling loss reduction can be attributed to a lowered temperature of burned gas adjacent to the combustion chamber walls by the leaner mixture there, formed by the stratification.…”

“…With a theoretical thermal efficiency η th of 0.575, which is for the compression ratio of ε=8.5 and the specific heat ratio of γ=1. 4, the values of the degree of constant volume η glh below 0.87 will cause the exhaust loss fraction φ ex to exceed the indicated thermal efficiency η i . The critical value of the degree of constant volume η glh , which results in η i /φ ex =1, increases with decreases in the theoretical thermal efficiency η th and compression ratio ε.…”

“…Such presence of leaner mixture implies that burned gas adjacent to the wall will be at a lower temperature. Previous research [4] using a constant volume combustion vessel has shown that a direct injection stratified charge is an effective technique to reduce the cooling loss in hydrogen combustion. Direct fuel injection, internal mixing of fuel and air, also has the advantage that it can avoid backfire, the flame propagation from combustion chamber to the intake pipe that may stop the engine.…”

Lean Hydrogen Combustion

“…These contradictory findings may be a result of differences in mixture formation. The view is based on the recent results of Shudo et al (2003), in which it was shown that with charge stratification such that the local mixture fraction in the near-wall region is expected to be lean compared to the bulk mixture, cooling losses can be decreased significantly and thermal efficiency increased. In order to take full advantage of the potential of the DI-H2ICE, a highpressure, high flow-rate hydrogen injector is required for operation at high engine speeds and to overcome the in-cylinder pressure for injection late in the compression stroke.…”

Mixture distribution measurement using laser induced breakdown spectroscopy in hydrogen direct injection stratified charge

“…Such presence of leaner mixture implies that burning gas adjacent to the walls is at a lower temperature and the heat transfer to the walls is decreased. A previous report showed this cooling loss reduction effect by direct injection stratified charge with hydrogen in a constant volume combustion chamber [10]. Compared to homogeneous combustion the stratified combustion reduces the cooling loss without deteriorating the degree of constant volume, and a cycle analysis shows an effective improvement in thermal efficiency [11].…”