The conventional crank-based internal combustion engine faces many challenges to remain a viable option for electric power generation. Limitations in mechanical, thermal, and combustion efficiencies must be overcome by innovations in existing technologies and progress toward new ones. The free piston linear engine (FPLE) has the potential to meet these challenges. Friction losses are reduced by avoiding rotational motion and linkages. Instead, electrical power is generated by the oscillation of the translator through a stator. Naturally, variable compression ratio provides a unique platform to employ advanced combustion regimes. However, possibly high variations in stroke length result in unknown dead center piston positions and greater difficulties in compression control as compared to conventional engines. Without control, adverse occurrences such as misfire, stall, over-fueling, and rapid load changes pose greater complications for stable system operation. Based on previous research, it is believed that incorporating springs will advance former designs by both increasing system frequency and providing a restoring force to improve cycle-to-cycle stability. Despite growing interest in the FPLE, current literature does not address the use of springs within a dual, opposed piston design. This investigation is an extension of recent efforts in the fundamental analysis of such a device. Previous work by the authors combined the dynamics of a damped, spring mass system with in-cylinder thermodynamic expressions to produce a closed-form nondimensional model. Simulations of this model were used to describe ideal Otto cycle as the equilibrium operating point. The present work demonstrates more realistic modeling of the device in three distinct areas. In the previous model, the work term was a constant coefficient over the length of the stroke, instantaneous heat addition (representing combustion) was only seen at top dead center (TDC) positions, and the use of the Otto cycle included no mechanism for heat transfer except at dead center positions. Instead, a position based sinusoid is employed for the work coefficient causing changes to the velocity and acceleration profiles. Instantaneous heat addition prior to TDC is allowed causing the compression ratio to decrease toward stable, Otto operation, and a simple heat transfer scheme is used to permit cylinder gas heat exchange throughout the stroke resulting in deviation from Otto operation. Regardless, simulations show that natural system stability arises under the right conditions. Highest efficiencies are achieved at a high compression ratio with minimal heat transfer and near-TDC combustion.

References

References
1.
Clark
,
N. N.
,
Nandkumar
,
S.
, and
Famouri
,
P.
,
1998
, “
Fundamental Analysis of a Linear Two-Cylinder Internal Combustion Engine
,”
SAE
Technical Paper No. 98269210.4271/982692.
2.
Atkinson
,
C. M.
,
Petreanu
,
S.
,
Clark
,
N. N.
,
Atkinson
,
R. J.
,
McDaniel
,
T. I.
,
Nandkumar
,
S.
, and
Famouri
,
P.
,
1999
, “
Numerical Simulation of a Two-Stroke Linear Engine-Alternator Combination
,”
SAE
Technical Paper No. 1999-01-092110.4271/1999-01-0921.
3.
Petreanu
,
S.
,
2001
, “
Conceptual Analysis of a Four-Stroke Linear Engine
,” Ph.D. dissertation,
West Virginia University
,
Morgantown, WV
.
4.
Clark
,
N.
,
McDaniel
,
T.
,
Atkinson
,
R.
,
Nandkumar
,
S.
,
Atkinson
,
C.
,
Petreanu
,
S.
,
Tennant
,
C.
, and
Famouri
,
P.
,
1998
, “
Modeling and Development of a Linear Engine
,”
Spring Technical Conference of the
ASME Internal Combustion Engine Division
, Fort Lauderdale, FL, Apr. 26–29, ICE-Vol. 30–2.
5.
Tóth-Nagy
,
C.
,
2004
, “
Linear Engine Development for Series Hybrid Electric Vehicles
,” Ph.D. dissertation,
West Virginia University
,
Morgantown, WV
.
6.
Van Blarigan
,
P.
,
Paradiso
,
N.
, and
Goldsborough
,
S.
,
1998
, “
Homogeneous Charge Compression Ignition With a Free Piston: A New Approach to Ideal Otto Cycle Performance
,”
SAE
Technical Paper No. 98248410.4271/982484.
7.
Van Blarigan
,
P.
,
2002
, “
Advanced Internal Combustion Electrical Generator
,”
Proceedings of the 2002 DOE Hydrogen Program Review
, National Renewable Energy Laboratory, Golden, CO, May 6–10, NREL Report No. NREL/CP-610-32405.
8.
Goldsborough
,
S. S.
, and
Van Blarigan
,
P.
,
2003
, “
Optimizing the Scavenging System for a Two-Stroke Cycle, Free Piston Engine for High Efficiency and Low Emissions: A Computational Approach
,”
SAE
Technical Paper No. 2003-01-000110.4271/2003-01-0001.
9.
Mikalsen
,
R.
, and
Roskilly
,
A. P.
,
2007
, “
A Review of Free-Piston Engine History and Applications
,”
Appl. Therm. Eng.
,
27
(
14–15
), pp.
2339
2352
.10.1016/j.applthermaleng.2007.03.015
10.
Mikalsen
,
R.
, and
Roskilly
,
A. P.
,
2010
, “
The Control of a Free-Piston Engine Generator—Part 1: Fundamental Analyses
,”
Appl. Energy
,
87
(
4
), pp.
1273
1280
.10.1016/j.apenergy.2009.06.036
11.
Mikalsen
,
R.
, and
Roskilly
,
A. P.
,
2010
, “
The Control of a Free-Piston Engine Generator—Part 2: Engine Dynamics and Piston Motion Control
,”
Appl. Energy
,
87
(
4
), pp.
1281
1287
.10.1016/j.apenergy.2009.06.035
12.
Robinson
,
M.
, and
Clark
,
N.
,
2014
, “
Fundamental Analysis of Spring-Varied, Free Piston, Otto Engine Device
,”
SAE Int. J. Engines
,
7
(
1
), pp.
195
220
10.4271/2014-01-1099.
13.
Fredriksson
,
J.
, and
Denbratt
,
I.
,
2004
, “
Simulation of a Two-Stroke Free Piston Engine
,”
SAE
Technical Paper No. 2004-01-187110.4271/2004-01-1871.
14.
Xiao
,
J.
,
Li
,
Q. F.
, and
Huang
,
Z.
,
2010
, “
Motion Characteristic of a Free Piston Linear Engine
,”
Appl. Energy
,
87
(
4
), pp.
1288
1294
.10.1016/j.apenergy.2009.07.005
15.
Mikalsen
,
R.
,
Jones
,
E.
, and
Roskilly
,
A. P.
,
2010
, “
Predictive Piston Motion Control in a Free-Piston Internal Combustion Engine
,”
Appl. Energy
,
87
(
5
), pp.
1722
1728
.10.1016/j.apenergy.2009.11.005
16.
Aichlmayr
,
H. T.
,
2002
, “
Design Considerations, Modeling, and Analysis of Micro-Homogeneous Charge Compression Ignition Combustion Free-Piston Engines
,” Ph.D. dissertation,
University of Minnesota
,
Minneapolis, MN
.
17.
Goldsborough
,
S. S.
, and
Van Blarigan
,
P.
,
1999
, “
A Numerical Study of a Free Piston IC Engine Operating on Homogeneous Charge Compression Ignition Combustion
,”
SAE
Technical Paper No. 1999-01-061910.4271/1999-01-0619.
18.
Van Blarigan
,
P.
,
Goldsborough
,
S.
,
Paradiso
,
N.
, and
Wu
,
J.
,
1998
,
Homogeneous Charge Compression Ignition Free Piston Linear Alternator
,
Sandia National Laboratories
,
Livermore, CA
.
19.
Martinez-Frias
,
J.
,
Aceves
,
S. M.
,
Flowers
,
D.
,
Smith
,
J. R.
, and
Dibble
,
R.
,
2000
, “
HCCI Engine Control by Thermal Management
,”
SAE
Technical Paper No. 2000-01-286910.4271/2000-01-2869.
20.
Dec
,
J. E.
,
2009
, “
Advanced Compression-Ignition Engines—Understanding the In-Cylinder Processes
,”
Proc. Combust. Inst.
,
32
(
2
), pp.
2727
2742
.10.1016/j.proci.2008.08.008
You do not currently have access to this content.