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Technical Paper

Electrical Force Effects on Spray Cooling

Initial results are reported for the effects of electrical body forces on heat transfer performance of an instrumented spray cooling experiment. Heat transfer performance is documented for ranges of electrode voltage, spray volume flow rate, and heater power level using a Thick Film Resistor heater. The heat transfer coefficient increases with increased spray flow rate, and also increases somewhat versus heat flux. Without the electrical body forces, different brass and PVC spray nozzles show significant variation in spray cooling performance (order of ±5-15%) whenever the nozzle is realigned. Changing the nozzle-to-heater spacing results in similar performance variations. Initial Kelvin force electrode designs show no improvement in heat transfer performance using FC-72, while a Coulomb force electrode geometry and a second-generation Kelvin force electrode design both show modest but consistent improvements (order of 10% in heat flux; order of 5% for Nusselt number) using HFE-7000.
Technical Paper

Low Temperature Combustion with Thermo-Chemical Recuperation

The key to overcoming Low Temperature Combustion (LTC) load range limitations is based on suitable control over the thermo-chemical properties of the in-cylinder charge. The proposed alternative to achieve the required control of LTC is the use of two separate fuel streams to regulate timing and heat release at specific operational points, where the secondary fuel, with different autoignition characteristics, is a reformed product of the primary fuel in the tank. It is proposed in this paper that the secondary fuel is produced using Thermo-Chemical Recuperation (TCR) with steam/fuel reforming. The steam/fuel mixture is heated by sensible heat from the engine exhaust gases in the recuperative reformer, where the original hydrocarbon reacts with water to form a hydrogen rich gas mixture. An equilibrium model developed by Gas Technology Institute (GTI) for n-heptane steam reforming was applied to estimate reformed fuel composition at different reforming temperatures.
Technical Paper

Quantification of Energy Pathways and Gas Exchange of a Small Port Injection SI Two-Stroke Natural Gas Engine Operating on Different Exhaust Configurations

This paper examines the energy pathways of a 29cc air-cooled two-stroke engine operating on natural gas with different exhaust geometries. The engine was operated at wide-open-throttle at a constant speed of 5400 RPM with ignition adjusted to yield maximum brake torque while the fueling was adjusted to examine both rich and lean combustion. The exhaust configurations examined included an off-the-shelf (OTS) model and two other custom models designed on Helmholtz resonance theory. The custom designs included both single and multi-cone features. Out of the three exhaust systems tested, the model with maximum trapping efficiency showed a higher overall efficiency due to lower fuel short-circuiting and heat transfer. The heat transfer rate was shown to be 10% lower on the new designs relative to OTS model.
Journal Article

Resonance of a Spring Opposed Free Piston Engine Device

Recent free piston engine research reported in the literature has included development efforts for single and dual cylinder devices through both simulation and prototype operation. A single cylinder, spring opposed, oscillating linear engine and alternator (OLEA) is a suitable architecture for application as a steady state generator. Such a device could be tuned and optimized for peak efficiency and nominal power at unthrottled operation. One of the significant challenges facing researchers is startup of the engine. It could be achieved by operating the alternator in a motoring mode according to the natural system resonant frequency, effectively bouncing the translator between the spring and cylinder, increasing stroke until sufficient compression is reached to allow introduction of fuel and initiation of combustion. To study the natural resonance of the OLEA, a numeric model has been built to simulate multiple cycles of operation.
Journal Article

Effect of Combustion Timing and Heat Loss on Spring-Assisted Linear Engine Translator Motion

The free piston linear engine has the potential to achieve high efficiency and might serve as a viable platform for robust implementation of low temperature combustion schemes (such as homogeneous charge compression ignition - HCCI) due to its ability to vary compression and stroke in response to cylinder and load events. A major challenge is control of the translator motion. Lack of geometric constraint on the piston leads to uncertainty about its top dead center position and timing. While combustion control depends on knowledge of the piston motion, the combustion event also affects the motion profile of the piston. To advance understanding of this coupled system, a numeric model was developed to simulate multiple cycles of a dual cylinder, spring assisted, 2-stroke HCCI, free piston linear engine generator.
Technical Paper

Experimental Investigation of a Natural Gas Lean-Burn Spark Ignition Engine with Bowl-in-Piston Combustion Chamber

On- and off-road heavy-duty diesel engines modified to spark-ignition natural gas operation can reduce U.S. dependence on imported oil and enhance national energy security. Engine conversion can be achieved through the addition of a gas injector in the intake manifold and of a spark plug in place of the diesel injector. This paper investigated combustion characteristics and engine performance at several lean-burn operating conditions that changed spark timing, mixture equivalence ratio, and engine speed, using methane as NG surrogate.