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Conventional crank-based engines are limited by mechanical, thermal, and combustion inefficiencies. The free piston of a linear engine generator reduces frictional losses by avoiding the rotational motion and crankshaft linkages. Instead, electrical power is generated by the oscillation of a translator through a linear stator. Because the free piston is not geometrically constrained, dead center positions are not specifically known. This results in a struggle against adverse events like misfire, stall, over-fueling, or rapid load changes. It is the belief that incorporating springs will have the dual benefit of increasing frequency and providing a restoring force to aid in greater cycle to cycle stability. For dual free piston linear engines the addition of springs has not been fully explored, despite growing interest and literature.

In 2007, US EPA implemented the rule that the crankcase emissions be added to the tailpipe emissions to determine the total emissions from a diesel engine if the crankcase were not closed, but few data exist to quantify crankcase emissions from earlier model diesel engines. This paper presents the results of a study on the measurement of the size distribution and number concentration of particulate matter (PM) emitted from the crankcase vents from four different diesel engines under different engine speeds and loads. The engines used in the study were a 1992 Detroit Diesel Series 60, a 1996 Caterpillar 3406E, a 1997 Cummins B5.9 and a 1995 Mack E7-400. The Detroit Diesel engine was tested on an engine dynamometer and crankcase and tailpipe particulates were observed at varying engine speeds and loads. The other three engines were mounted in vehicles, and crankcase PM was observed at several engine speeds with no external load.

Natural Gas engines are viewed as an alternative to diesel power in the quest to reduce heavy duty vehicle emissions in polluted urban areas. In particular, it is acknowledged that natural gas has the potential to reduce the inventory of particulate matter, and this has encouraged the use of natural gas engines in transit bus applications. Extensive data on natural gas and diesel bus emissions have been gathered using two Transportable Heavy Duty Vehicle Emissions Testing Laboratories, that employ chassis dynamometers to simulate bus inertia and road load. Most of the natural gas buses tested prior to 1997 were powered by Cummins L-10 engines, which were lean-burn and employed a mechanical mixer for fuel introduction. The Central Business District (CBD) cycle was used as the test schedule.

Research at West Virginia University has led to the development of a novel crankless reciprocating internal combustion engine. This paper presents a time-based model used to investigate the performance of two-stroke direct injection compression ignition linear engines. The two-stroke linear engine consists of two pistons, linked by a connecting rod, that are allowed to move freely in response to changes in the engine's fueling and load across the full operating cycle of the engine. The computer model uses a combination of a series of dynamic and thermodynamic numerical equations, which have been solved to provide a detailed analysis of the two-stroke direct injection linear engine operation. Parameters such as rate of combustion, convection heat transferred inside the cylinders, friction forces, external loads, acceleration, velocity profile, compression ratio, and in-cylinder pressures were modeled.

With continuously increasing concern for the emissions from two-stroke engines including regulated hydrocarbon (HC) and oxides of nitrogen (NOx) emissions, non-road engines are implementing proven technologies from the on-road market. For example, four stroke diesel generators now include additional internal exhaust gas recirculation (EGR) via an intake/exhaust valve passage. EGR can offer benefits of reduced HC, NOx, and may even improve combustion stability and fuel efficiency. In addition, there is particular interest in use of natural gas as fuel for home power generation. This paper examines exhaust throttling applied to the Helmholtz resonator of a two-stroke, port injected, natural gas engine. The 34 cc engine was air cooled and operated at wide-open throttle (WOT) conditions at an engine speed of 5400 RPM with fueling adjusted to achieve maximum brake torque. Exhaust throttling served as a method to decrease the effective diameter of the outlet of the convergent cone.

When heavy-duty truck emissions are expressed in distance-specific units (such as g/mile), the values may depend strongly on the nature of the test cycle or schedule. Prior studies have compared emissions gained using different schedules and have proposed techniques for translating emissions factor rates between schedules. This paper reviews emissions data from the 5-mode CARB HHDDT Schedule, UDDS Schedule, and a steady-state cycle (AC5080), with reference to each other. NOX and PM emissions are the two components of emissions which are reviewed. A heavy-duty chassis dynamometer was used for emissions characterization along with a full scale dilution tunnel. The vehicle test weights were simulated at 30,000 lbs, 56,000 lbs, and 66,000 lbs. For each vehicle, average data from one mode or cycle have been compared with average data for a different mode or cycle.

Compression and power stroke cycles for a 4 stroke cycle spark ignition engine modified by extending the connecting rod to simulate purely sinusoidal piston motion are analyzed over a range of operating speeds and are compared with those of a similar conventional engine. Heat release rate is estimated for both engines using a simple Wiebe function with the functional parameters found via a simplex curve fitting method used in conjunction with experimental pressure curves. It is shown that the functional parameters which represent the combustion and the duration of fuel burn are slightly larger over the range of operation in the sinusoidal engine while the shape factor remains largely the same. However, the pressure-crank angle curves are sufficiently similar such that conventional slider-crank curves can be used to model sinusoidal engines, which was the motivation behind this research.

With few exceptions most internal combustion engines use a slider-crank mechanism to convert reciprocating piston motion into a usable rotational output. One such exception is the Stiller-Smith Mechanism which utilizes a kinematic inversion of a Scotch yoke called an elliptic trammel. The device uses rigid connecting rods and a floating/eccentric gear train for motion conversion and force transmission. The mechanism exhibits advantages over the slider-crank for application in internal combustion engines in areas such as balancing, size, thermal efficiency, and low heat rejection. An overview of potential advantages of an engine utilizing the Stiller-Smith Mechanism is presented.

The Stiller-Smith mechanism is a new mechanism for the translation of linear motion into rotary motion, and has been considered as an alternative to the conventional slider-crank mechanism in the design of internal combustion engines and piston compressors. Piston motion differs between the two mechanisms, being perfectly sinusoidal for the Stiller-Smith case. Plots of dimensionless volume and volume rate-change are presented for one engine cycle. It is argued that the different motion is important when considering rate-based processes such as heat transfer to a cylinder wall and chemical kinetics during combustion. This paper also addresses the fact that a Stiller-Smith engine will be easier to configure for adiabatic operation, with many attendant benefits.

Linear engine alternator (LEA) design optimization traditionally has been difficult because each independent variable alters the motion with respect to time, and therefore alters the engine and alternator response to other governing variables. An analogy is drawn to a conventional engine with a very light flywheel, where the rotational speed effectively is not constant. However, when springs are used in conjunction with an LEA, the motion becomes more consistent and more sinusoidal with increasing spring stiffness. This avoids some attractive features, such as variable compression ratio HCCI operation, but aids in reducing cycle-to-cycle variation for conventional combustion modes. To understand the cycle-to-cycle variations, we have developed a comprehensive model of an LEA with a 1kW target power in MATLAB®/Simulink, and an LEA corresponding to that model has been operated in the laboratory.

The control and design optimization of a Free Piston Engine Generator (FPEG) has been found to be difficult as each independent variable changes the piston dynamics with respect to time. These dynamics, in turn, alter the generator and engine response to other governing variables. As a result, the FPEG system requires an energy balance control algorithm such that the cumulative energy delivered by the engine is equal to the cumulative energy taken by the generator for stable operation. The main objective of this control algorithm is to match the power generated by the engine to the power demanded by the generator. In a conventional crankshaft engine, this energy balance control is similar to the use of a governor and a flywheel to control the rotational speed. In general, if the generator consumes more energy in a cycle than the engine provides, the system moves towards a stall.

In 2007, the Environmental Protection Agency will begin measuring not only exhaust emissions from diesel engines, but also emissions from the crankcase if it is not vented into the engine intake. The 2007 government standards for emissions of carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOx) and particulate matter (PM) will also become more restrictive. There is the additional concern that crankcase emissions from present day trucks and buses may impact the quality of air inside the vehicle. This paper presents data to characterize crankcase emissions and examines a crankcase emissions abatement system (CEAS), the New Condensator®, manufactured by World NCI. Rather than allowing crankcase emissions to leave via a vent tube, a CEAS re-circulates the emissions to the intake of the engine.