A Compact Pollution-Free
External Combustion Engine
with High Part-Load Efficiency
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2. Motivations For This Engine
There is an urgent need for vehicle engines that can efficiently
and cleanly burn other fuels besides refined petroleum. Only then will
the incentive arise to develop such fuels on a commercial scale. The Age
of Petroleum will end in about 40 years at current consumption [5,6,7],
unless new deposits are discovered or consumption is reduced.
Petroleum used in transportation accounts for 31% of the
carbon dioxide emissions in the US [8].
Engines with higher efficiency under normal operation could reduce that.
Road vehicles generally run at only a small fraction of their peak power.
The extra power is needed for acceleration and grade climbing. Internal
combustion engines have throttling and pumping losses at low loads that
reduce efficiency. Steam engines avoid this, and the engine presented
here actually has higher efficiency at part load than at full power.
The fuel for external combustion engines needs less processing
and refining. This ultimately reduces total energy use and overall emissions
from the source (e.g., the oil well) to the tailpipe. There are other
options such as plug-in hybrids or pure electric vehicles. But over 80%
of the fossil-fueled electricity in the US is generated by burning coal
[8]. It can be shown [9]
that charging vehicle batteries with electricity from coal plants actually
increases carbon emissions.
There is also the problem of localized pollution due to
nitrous oxides, unburned fuel emissions, and carbon monoxide. This is
especially serious in urban areas; and ways to reduce it must be sought.
Considering all of the above, external combustion engines
appear especially attractive. That appeal is even greater for the engine
presented here, as will be shown in detail below.
In external combustion engines the working fluid and combustion
gases are separate and can be individually optimized. In Rankine-type
external combustion engines, the fluid being recompressed is liquid rather
than gas. This reduces the work of recompression, which increases net
output and thereby reduces the peak temperature needed for a given efficiency.
Many different working fluids have been explored by others [10]
and, to a lesser extent, by the author. But, all things considered, steam
turns out to be the best.
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