Effect of Negative Valve Overlap on Combustion and Emissions of CNG-Fueled HCCI Engine with Hydrogen Addition

Abstract

In order to study the effect of negative valve overlap on combustion and emission characteristics of a homogeneous charge compression ignition engine fueled with natural gas and hydrogen, the test and the simulation were conducted using an engine cycle model coupling the chemical kinetic reaction mechanism under different valve timing conditions. Results show that the internal EGR formed by using negative valve overlap could heat the inlet mixtures and improve the spontaneous ignition characteristic of the engine. The residual exhaust gas could slow down the heat release rate, decrease the pressure rise rate and the maximum combustion temperature, and reduce the NOx emission simultaneously. Among the three NVO schemes, the strategy of changing the intake valve opening timing individually can create the least power loss, and the symmetric NVO strategy which changes both the exhaust valve closing timing and the intake valve opening timing simultaneously can achieve the best heating effect of inlet mixtures and the satisfactory decrease of combustion temperature, as well as the largest reduction of NOx emission.

Hydrogen as Fuel for ICEs: State of Art and Technological Challenges

“…Hydrogen shortened the fame development, increasing the thermal efciency and mean efective pressure (i) Termal efciency (ii) Lean burn strategies [28] 2015 Infuence of spark timing on the performance and emission characteristics of gasoline-hydrogen-blended high-speed spark-ignition engine Experimental investigation Spark timing turned out to be a key factor for the thermal efciency, shifting the combustion towards the TDC (i) Ignition timing infuence (ii) NOx and CO emissions [29] 2021 Efect of negative valve overlap on combustion and emissions of CNG-fuelled HCCI engine with hydrogen addition Experimental investigation Symmetric NVO strategy can achieve the highest EGR rate easing the HRR and reducing the PRR, which improves the rough running of HCCI engine, preventing the occurrence of knocking (i) Valve timing efect (ii) NOx emissions [30] 2022 Efects of gasoline and hydrogen blends on exhaust gas emissions and fuel consumption from gasoline internal combustion engines…”

“…More in detail, keeping the hydrogen content to 10% in volume fraction, it was possible to increase the mean efective pressure and thermal efciency by 10% and 4.0-4.5%, respectively. Other studies evaluated the efect of the typical engine combustioncontrolling factors such as spark ignition timing and valve timing [28,29] on the extension of the optimal operating range of hydrogen-gasoline blends. Te spark timing plays a key role in advancing the combustion process close to the TDC and then improving the thermal efciency and fuel consumption, while most of the investigations on the valve timing clearly showed the benefts of anticipating the intake valve opening (IVO) for medium-and high-load conditions in order to increase the volumetric efciency, while at low load, this efect results quite limited.…”

A Review of Low-CO2 Emission Fuels for a Dual-Fuel RCCI Engine

“…These parameters have the greatest impacts on the level of swirling of the fuel-air mixture, which for different fuel mixtures has different impacts on efficiency. The operation of an engine with HCNG fuel, compared to the use of a standard engine with a timing system (negative valve overlaps), designed for operation with conventional fuels such as diesel or gasoline, lessens the efficiency of using the alternative fuel, that is, HCNG, as shown in [83]. Only the effects of the use of a double pilot dose in dual-fuel engines have been investigated [84].…”