Abstract
Establishing the homogeneous charge compression ignition (HCCI) process in a diesel engine, in order to improve exhaust emission quality while extending the HCCI regime, is one of the challenges in applying HCCI in worldwide applications. This can be done by decreasing the compression ratio, and controlling the exhaust gas recirculation (EGR) rate and charging temperature. In this paper, an original single cylinder diesel engine was converted to n-heptane-fueled HCCI with the fuel injected into the intake manifold. At the designed compression ratio of 20:1, the HCCI engine could operate stably at low speed (from 1600 rpm to 2000 rpm) and low load (10% to 20% load). In addition, reducing the compression ratio from 20:1 to 14.87:1 by changing the thickness of the cylinder head gasket and with no EGR applied extended the operating range to 50% load and 3200 rpm speed.
Highlights
In order to align with future emissions and greenhouse gas legislation for internal combustion engines, research efforts are focused on the mixing process and in-cylinder combustion together with costly and advanced after-treatment devices
SOC1 and SOC2 were designated as the start of combustion locations for low-temperature oxidation (LTO) and high-temperature oxidation (HTO), respectively
The starts of combustion (SOC) can be calculated as 10% of the cumulative heat release location, or it can be the derivative of the Rate of Heat Release (ROHR) versus crank angle
Summary
In order to align with future emissions and greenhouse gas legislation for internal combustion engines, research efforts are focused on the mixing process and in-cylinder combustion together with costly and advanced after-treatment devices. Due to its operating characteristics, the operating HCCI engine range is restricted by an excessive pressure rise rate in high load region, which causes engine knock To solve this problem, the gas temperature should be controlled properly by retarding ignition timing after top dead center (TDC) [5]. Many issues have been addressed recently regarding HCCI combustion such as control of ignition timing, widening the HCCI operation range to high loads, and reducing the carbon monoxide (CO) and hydrocarbons (HC) emissions [9] Systems such as hot EGR [10], variable compression ratio (VCR) [11], and variable valve actuation (VVA) [12] show promise for these purposes, while for high engine load operation, intake pressure boosting can be used [13].
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