Effects of various intake valve timings and spark timings on combustion, cyclic THC and NOX emissions during cold start phase with idle operation in CVVT engine

Abstract

In a gasoline SI engine, valve events and spark timings put forth a major influence on overall efficiency, fuel economy, and exhaust emissions. Residual gases controlled by the valve overlap can be used to reduce NOx emissions and the spark retardation technique can be used to improve raw THC emissions and catalyst light-off performance during the cold start phase. This paper investigated the behaviors of the engine and its combustion characteristics with various intake valve timings and spark timings during the fast idle condition and cold start. And cyclic THC and NOx emissions were measured at the exhaust port and their formation mechanisms were examined with fast response gas analyzers. As a result, THCs and NOx were reduced by 35% and 23% with optimizing valve overlap and spark advance during the cold transient start phase. Consequently, the valve events and ignition timings were found to significantly affect combustion phenomena and cold-start emissions.

Effect of Valve Timing and Excess Air Ratio on Torque in Hydrogen-Fueled Internal Combustion Engine for UAV

“…It is general, to advance the opening timing to a BTDC point so that as much intake air as possible can be introduced, since the flow rate of the intake air is not fast at low engine speed. [26,27]. The influence of changing the valve opening time at the excess air ratio of 1.25, which can stably obtain higher torque, was investigated.…”

Modelling and Fuzzy-Threshold Control of SI Engine for Emission Reduction during Cold Start Phase

“…This results in the exhaust gas recirculation (EGR) rate. This method leads to reduction of NOx and HC emissions and accelerate warming up of inlet manifold, which in turn helps to homogenize the fuel mixture for better combustion [13,[21][22][23][24]. In addition, the increase in VO improves engine volumetric efficiency at higher engine speeds than normal idle engine speed and consequently increases engine efficiency and increase engine speed [19].…”

“…Therefore, by increasing the VO during the catalyst warm-up phase, the engine efficiency and engine speed can be increased more efficiently. Now, we may use this efficiency factor, to apply more retardation of the ignition angle and to accelerated catalyst warm-up phase [21], and reduce HC emission [13,25].…”

“…This controller is switched "ON" after in cold start condition and after passing the transient initial overshoot and undershoot and when the engine speed increases to above a certain threshold (1250 rpm). During "ON" condition, the controller increases the VO, which increases the engine speed, and reduces NOx and HC emissions [13]. Next, the fuzzy control strategy is applied to the ignition angle to increase combustion gas temperature.…”

“…Using VVT system and the VO mechanism, especially in the cold start phase, the volumetric efficiency of the engine is increased, and thus the engine speed and exhaust gases flow are increased, and the catalytic converter is heated up faster and reduce cumulative exhaust emissions. Besides, the EGR (exhaust gas recirculation) can be applied with proper control of this system and therefore NOx and HC harmful emissions are reduced [13,14]. This control strategy is applied in the form of a controller called the fuzzy controller to the model.…”