Search Results

A rapid compression/expansion machine (RCEM) based on a single-cylinder engine was developed to understand the fundamental phenomenon of knock during spark-ignition (SI) combustion. In order to cause auto-ignition in the end-gas mixture during the flame-propagation process, and also to visualize the processes, the original head of the engine was replaced with a specially designed combustion chamber. The effects of spark timing, compression ratio and equivalence ratio on knock intensity were systematically investigated using the RCEM with n-butane fuel. In addition, the possibility of knock control by the injection of hydrogen into the end-gas region is also discussed. The experimental results indicate that a higher compression ratio, spark-ignition timing at -10 °ATDC and a stoichiometric equivalence ratio cause heavy knock. However, the knock intensity is drastically decreased with hydrogen injection.

The aim of this study is to find strategies for fully utilizing the advantage of diesel-ethanol blend fuel in recent diesel engines. For this purpose, experiments were performed using a single-cylinder direct injection diesel engine equipped with a high-pressure common rail injection and a cold EGR system. The results indicate that significant PM reduction at high engine loads can be achieved using 15% ethanol-diesel blend fuel. Increasing injection pressure promotes PM reduction. However, poor ignitability of ethanol blended fuel results in higher rate of pressure rise at high engine loads and unstable and incomplete combustion at lower engine loads. Using pilot injection with proper amount and timing solves above problems. NOx increase due to the high injection pressure can be controlled employing cold EGR. Weak sooting tendency of ethanol-blend fuel enables to use high EGR rates for significant NOx reduction.

Utilizing the desirable feature of hydrogen, this study demonstrates the improvement of engine performance and exhaust emissions due to the mixing of hydrogen into natural-gas fuel in a spark-ignition engine at the wide-open throttle (WOT) condition. Both hydrogen and natural-gas fuels were injected into the intake port only in the suction flow, which could make the operation under a wide range of conditions without backfire even at a hydrogen fuel. Based on the measured processes of combustion, the knock characteristics were discussed with special attention to the extremely high burning velocity of hydrogen. At a higher compression ratio, the thermal efficiency in the stoichiometric condition was improved, nevertheless a precise control of ignition timing was required to suppress a hard knock. From the experimental results of engine performance in a variety of parameters, optimal use of hydrogen was exhibited for different engine loads.