Page 55 - ASME DSCC 2015 Program

Technical Program

A new Approach to Reduce Engine-out Emissions Enabled by A Phenomenological Model for Predicting Combustion Phasing and
Trajectory-Based Combustion Control Variability of Spark Assisted Compression Ignition (SACI) Engines
Invited session paper. DSCC2015-9838 Invited session paper. DSCC2015-9883
Chen Zhang, University of Minnesota Twin Cities Campus, Minneapolis, MN, niket Prakash, Jason B., Martz, Anna G. Stefanopoulou, University of
United States, Zongxuan Sun, University of Minnesota, Minneapolis, MN, Michigan, Ann Arbor, MI, United States
United States
An advanced combustion mode, Spark Assisted Compression Ignition (SACI)
Previously, the authors have proposed the concept of piston trajecto- has shown the ability to extend loads relative to Homogenous Charge Com-
ry-based combustion control enabled by free piston engines (FPE). With this pression Ignition (HCCI) but at lower than fuel efficiency. SACI combustion is
novel control method, the FPE realizes in-cycle real-time combustion control, initiated by a spark followed by a rapid autoignition (HCCI-like combustion)
in terms of adjusting the ignition timing and manipulating the in-cylinder of the remaining fraction of the fuel. Extending previous work the coeffi-
temperature trace, through various piston trajectories and achieves higher cients of the Wiebe function used to fit the two combustion phases, are here
thermal efficiency compared to the conventional internal combustion en- regressed as functions of the air path variables and actuator settings. The
gines. In this paper, the effects of this new combustion control on engine-out parameterized regression model enables the interpretation of the combus-
emissions are studied. First, a model is developed that includes different pis- tion model with manifold filling dynamics, which are essential for meanvalue
ton trajectories in the FPE, a convective heat loss sub model and a reduced modeling and model-based control of combustion phasing. SACI combus-
n-heptane reaction mechanism with major emissions species from diesel en- tion, however exhibits high cyclic variability with random characteristics.
gines. Afterwards, a new approach which reduces the engine-out emissions Thus, control of combustion phasing needs to account for the cyclic variabil-
by employing novel piston trajectories is described. At last, analyses of the ity to correctly fit the phasing data. This paper also documents the success
simulation results demonstrating the variable piston trajectories’ effects on of regressing the cyclic variability (standard deviation) at various operating
CO and NOx emissions are presented, which further reveal the advantages conditions as again a function of air path variables and actuator settings. The
of the trajectory-based combustion control. combination of the two models is a breakthrough in predicting the mean-val-
Is It Economical to Ignore the Driver? A Case Study on Multimode ue engine behavior and the random statistics of the cycle-to-cycle variability.
Combustion Control of the Intake Air Dynamics on a Single-Cylinder Engine, to
Invited session paper. DSCC2015-9875 Replicate Multi-Cylinder Engine Dynamics
Sandro P. nuesch, Anna G. Stefanopoulou, University of Michigan, Ann Invited session paper. DSCC2015-9960
Arbor, MI, United States John J. Moskwa, PCRL, University of Wisconsin-Madison, Madison, WI,
Ignoring the driver’s torque command can be beneficial for fuel economy, United States, Mark B. Murphy, Sargent & Lundy, Chicago, IL, United
States
especially if it leads to extended residence time at efficient operating condi-
tions. We answered this question for a particular engine, which allows mode Single-cylinder test engines are used extensively in engine research, and
switches between spark ignition (SI) and homogeneous charge compression sparingly in engine development, as an inexpensive way to test or evaluate
ignition (HCCI) new concepts or to understand in-cylinder motion or combustion. They also
allow good access to the cylinder for instrumentation, however, these
combustion. When operating such a multimode combustion engine it might
single-cylinder engines differ significantly in rotational dynamics, gas intake
be required to defer a load command outside the feasible regime of one
dynamics, heat transfer dynamics, dynamic coupling between cylinders, and in
combustion mode until a mode switch is accomplished. The resulting delays
other areas. Charge motion within the cylinder, even during the closed period
in engine torque response might negatively affect vehicle performance and
differs from the multi-cylinder engine because of the differences in both
drivability. In this paper a longitudinal vehicle model is presented, which
instantaneous flow and momentum.
incorporates dynamics associated with SI/HCCI mode switching. Two exem-
Researchers in the Powertrain Control Research Laboratory (PCRL) at the
plary supervisory control strategies were evaluated in terms of fuel economy
University of Wisconsin-Madison have developed single-cylinder engine transient
and torque behavior. It was seen that the duration of a mode switch may
test systems that control the instantaneous dynamic cylinder boundary conditions
be short enough to avoid substantial impairment in torque response. This
to replicate those in the target multi-cylinder engine. The overall goal is to exploit
in turn would lead to the opportunity of purposefully ignoring the driver
the benefits of the single-cylinder engine, while eliminating the negative aspects
command. Thereby, the residence time in the beneficial HCCI combustion
of this device, and to have the single-cylinder ‘think’ it is dynamically operating
regime is prolonged and fuel-expensive mode switching avoided. The result
within a multi-cylinder engine.
is a trade-off between torque deviation and improvements in fuel econo-
This paper describes the latest developments in controlling the intake gas dy-
my. Finally, based on this trade-off the supervisory control strategy relying
namics of the single-cylinder engine to meet these goals. A combination of both
on a short-term prediction of engine load was seen to achieve similar fuel
rotary and proportional valves are used to accurately replicate the instantaneous
economy with slightly improved torque response than a strategy without
intake airflow that exists in the multi-cylinder engine, including during transients.
prediction.
A Fourier-based approach instead of the previous time-based trajectory control is
used to accomplish these goals. This is a third generation of intake air simulator
(IAS3) that is a significant step forward in both simplifying the system, and in signifi-
cantly expanding the operating envelop of the engine to include the full engine
operating range of the multi-cylinder engine. A brief introduction of the entire
transient test system will show the reader how rotational, heat transfer, and gas 55
dynamics are controlled, and how the IAS3 fits into this overall system.