Knock and Emission Characteristics of Heavy-Duty HCNG Engine with Modified Compression Ratios 2013-01-0845
Reduction of carbon dioxide (CO₂) emission, which causes global
warming, is an important guideline for vehicle engine development.
There are two types of methods for reducing the CO₂ emission of a
vehicle engine. The first involves improving engine efficiency. The
second involves the use of a low-carbon fuel, i.e., fuel with high
hydrogen to carbon ratio. Hydrogen-compressed natural gas blend
(HCNG) has been researched as a low-carbon fuel. Given that thermal
efficiency of an engine cycle increases with its compression ratio
(CR), an HCNG engine with high compression ratio not only has high
efficiency but also low CO₂ emission. However, unexpected
combustion such as knock could occur owing to the increased CR.
In this study, we investigated the knock and emission
characteristics of an 11-L heavy-duty HCNG engine with a modified
CR. A conventional CNG engine was fuelled with HCNG30 (CNG 70 vol%
and hydrogen 30 vol%). The engine was operated at 1,260 rpm, under
the wide open throttle condition, and with CRs of 10.5 and 11.5.
The results showed that under a CR of 11.5, the engine's knock
margin decreased because of higher in-cylinder pressure and
temperature. Thermal efficiency improved with the increased CR,
which caused a significant decrease in CO₂ emission. However,
NOx emission increased slightly at a certain excess