Homogeneous Charge Compression Ignition with a Free Piston: A New Approach to Ideal Otto Cycle Performance

Abstract

Sandia National Laboratories has been investigating a new, integrated approach to generating electricity with ultra low emissions and very high efficiency for low power (30 kW) applications such as hybrid vehicles and portable generators. Our approach utilizes a free piston in a double-ended cylinder. Combustion occurs alternately at each cylinder end, with intake/exhaust processes accomplished through a two stroke cycle. A linear alternator is mounted in the center section of the cylinder, serving to both generate useful electrical power and to control the compression ratio by varying the rate of electrical generation. Thus, a mechanically simple geometry results in an electronically controlled variable compression ratio configuration. The capability of the homogeneous charge compression ignition combustion process employed in this engine with regards to reduced emissions and improved thermal efficiency has been investigated using a rapid compression expansion machine. Eight different fuels, including propane, natural gas, hydrogen, methanol, n-pentane, hexane, n-heptane, and isooctane have been used at low equivalence ratio (φ ~ 0.35) and initial temperatures of 25°C, 50°C and 70°C. The results indicate that the cycle thermal efficiency can be significantly improved (56% measured) relative to current combustion systems, while low NO x emissions are possible (<10 PPM). HC and CO emissions must be controlled through some aftertreatment technology. The primary cause of

Homogeneous Charge Compression Ignition with Water Injection

“…Several studies on four stroke engines have also been carried out [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. High efficiency and low NOxemissions are reported, but emissions of unburned hydrocarbons are high.…”

Effect of Motoring Voltage on Compression Ratio of a Free-Piston Linear Generator Engine

“…This reduces heat loss and lowers the combustion temperature, thus producing low NOx. Van Blarigan [9] measured the thermal efficiency of an FPLG at 56% with low NOx emissions compared with the conventional crank engine whose efficiency is lower than 40%. Fredriksson [10] found similar characteristics and showed that most combustion occurred at fast expansion rate and below 1800 K which is enough to ensure an ultra-low level of NOx.…”

Homogeneous Charge Compression Ignition Free Piston Linear Alternator

“…Figures 24,25, and 26 show the results for n-heptane. An equivalence ratio of 0.334 and an initial temperature of 24OC were used.…”

“…An equivalence ratio of 0.321 was used at initial temperatures of 25 and 7OoC. Isooctane, like propane and natural gas, burned in a single step process and at nearly constant volume, as can be seen in Figure 27.…”