Simulation of CNG Engine in Agriculture Vehicles. Part 2: Coupled
Engine and Exhaust Gas Aftertreatment Simulations Using a Detailed TWC
Model
Authors: Leon de Syniawa Larisa , Siddareddy Reddy Babu , Prehn Sascha , Guenther Vivien , Franken Tim , Buchholz Bert , Mauß Fabian 
Published: August 2023

<div class="section abstract"><div class="htmlview paragraph">In more or less all aspects of life and in all sectors, there is a generalized
global demand to reduce greenhouse gas (GHG) emissions, leading to the
tightening and expansion of existing emissions regulations. Currently, non-road
engines manufacturers are facing updates such as, among others, US Tier 5
(2028), European Stage V (2019/2020), and China Non-Road Stage IV (in phases
between 2023 and 2026). For on-road applications, updates of Euro VII (2025),
China VI (2021), and California Low NOx Program (2024) are planned. These new
laws demand significant reductions in nitrogen oxides (NOx) and particulate
matter (PM) emissions from heavy-duty vehicles. When equipped with an
appropriate exhaust aftertreatment system, natural gas engines are a promising
technology to meet the new emission standards. Gas engines require an
appropriate aftertreatment technology to mitigate additional GHG releases as
natural gas engines have challenges with methane (CH<sub>4</sub>) emissions that
have 28 times more global warming potential compared to CO<sub>2</sub>. Under
stoichiometric conditions a three-way catalytic converter (TWC - stoichiometric
combustion) can be used to effectively reduce emissions of harmful pollutants
such as nitrogen oxides and carbon monoxide (CO) as well as GHG like
methane.</div><div class="htmlview paragraph">The aim of the present study is to understand the performance of the catalytic
converter in function of the engine operation and coolant temperature in order
to optimize the catalyst operating conditions. Different cooling temperatures
are chosen as the initial device temperature highly affects the level of warm up
emissions such that low coolant temperatures entail high emissions. In order to
investigate the catalyst performance, experimental and virtual transient engine
emissions are coupled with a TWC model to predict tail-pipe emissions at
transient operating conditions. Engine experiments are conducted at two initial
engine coolant temperatures (10°C and 25°C) to study the effects on the Non-Road
Transient Cycle (NRTC) emissions. Engine simulations of combustion and emissions
with acceptable accuracy and with low computational effort are developed using
the Stochastic Reactor Model (SRM). Catalyst simulations are performed using a
1D catalytic converter model including detailed gas and surface chemistry. The
initial section covers essential aspects including the engine setup, definition
of the engine test cycle, and the TWC properties and setup. Subsequently, the
study introduces the transient SI-SRM, 1D catalyst model, and kinetic model for
the TWC. The TWC model is used for the validation of a NRTC at different coolant
temperatures (10°C and 25°C) during engine start. Moving forward, the next
section includes the coupling of the TWC model with measured engine emissions.
Finally, a virtual engine parameter variation has been performed and coupled
with TWC simulations to investigate the performance of the engine beyond the
experimental campaign. Various engine operating conditions (lambda variation for
this paper) are virtually investigated, and the performance of the engine can be
extrapolated. The presented virtual development approach allows comprehensive
emission evaluations during the initial stages of engine prototype
development.</div></div>