Modeling of Three-Way Catalyst Dynamics for a Compressed Natural Gas Engine during Lean–Rich Transitions

Experimental investigation on particulate filters for heavy-duty natural gas engines: Potentialities toward EURO VII regulation

The urgent need to meet the stringent regulation requirements on sub-23 nm particles emissions is pushing the interest towards efficient strategies for their reduction, involving different propulsive technologies, including the Natural Gas engines. Although considered as particulate matter-free, the growing diffusion of Natural Gas Heavy-Duty engines as a key element in the low-term towards decarbonization, requires their compliance with upcoming regulations. The use of particulate filters, in combination with the Three-Way Catalyst (TWC), could represent a promising and viable solution to achieve high conversion of gas-phase criteria pollutants and high particles filtration efficiency. The present activity arose from a collaboration among research groups of CNR-STEMS, FPT Industrial and NGK Europe GmbH, two industrial companies leaders in the topics here addressed. Target of the work is the evaluation of the potentiality offered by the use of filters in the abatement of particles emitted by a Natural Gas engine. Particles number, mass and size distribution analysis have been performed over the World Harmonized Transient Cycles. The exhaust line was properly designed to foresee the installation of particulate filter downstream a conventional TWC, in a close-coupled configuration. The filtration efficiency of two filters, from hereon termed as CNG Particulate Filters (CPFs), with different wall thickness and cell structures and a filter with catalytic coating, was compared. High particle abatement efficiency was found for all the filters, with values close to 90%, without noticeable increases in backpressures. The CPF with standard porosity showed the best performance, while no further significant benefits were found with the addition of a catalytic coating. The performed analysis places in an important emphasis in view of the forthcoming EURO VII regulations on PN limits (PN₁₀) and sets the basis and direction for further optimization in filter material properties and catalyst coating in meeting stringent PN emission targets.

Effect of Operating Conditions and TWC Parameters on Emissions Characteristics of a Stoichiometric Natural Gas Engine

This study involved conducting an experimental and numerical investigation on the effects of the air-to-fuel ratio (AFR), engine speed, and engine load on the inlet gas component of a three-way catalyst (TWC) and on the effects of noble metal loading, noble metal ratio, and carrier pore density on the emission conversion efficiency. The results showed that AFR can significantly affect the raw emissions of NOx and total hydrocarbon (THC), and better emission conversion efficiency of a TWC can be reached when AFR is controlled between 0.995 to 1. Compared with engine speed, engine load has a relatively small effect on exhaust temperature but greatly affects the flow velocity and NOx and THC emissions. Increasing the content of Pt in the catalyst can improve the THC conversion efficiency. For low Pt and Pd-Rh catalysts, the THC conversion effect is significantly deteriorated. The content of Rh affects the NOx conversion, and NOx conversion efficiency at high speeds is significantly reduced when Rh content is reduced. Higher carrier pore density can slightly improve the catalytic reaction rate and emission conversion efficiency at high engine speeds. However, high conversion efficiency can be maintained even after aging.

Comparative Study of Powertrain Hybridization for Heavy-Duty Vehicles Equipped with Diesel and Gas Engines

This article describes a study that aimed to estimate the fuel-saving potential possessed by the hybridization of conventional powertrains intended for heavy-duty vehicles based on diesel and natural gas fueled engines. The tools used for this analysis constitute mathematical models of vehicle dynamics and the powertrain, including its components, i.e., the engine, electric drive, transmission, and energy storage system (ESS). The model of the latter, accompanied by experimental data, allowed for an analysis of employing a supercapacitor regarding the selection of its energy content and the interface between the traction electric drive and the ESS (in light of the wide voltage operating range of supercapacitors). The results revealed the influence of these factors on both the supercapacitor efficiency (during its operation within a powertrain) and the vehicle fuel economy. After implementation of the optimized ESS design within the experimentally validated vehicle model, simulations were conducted in several driving cycles. The results allowed us to compare the fuel economy provided by the hybridization for diesel and gas powertrains in different driving conditions, with different vehicle masses, taking into account the onboard auxiliary power consumption.