The trucking industry is responsible for a lot of pollution in the air we breathe in the country. From the studies done in 2013 by environmental groups, it is estimated that the industry consumed about 2.7 million barrels of fuel every day and emitted an overwhelming 530 million metric tons of carbon dioxide, equivalent to 13.5% of the country’s total emissions in the year.
As the issue of global warming is getting more relevant than ever, it puts the industry in a spot, as reducing even a fraction of the emission output could do the surroundings a world of good. The government on its part is tightening its screws as environmental agencies direct fleets to run trucks that adhere to stricter emission standards.
Ricardo, a global strategic engineering and environmental consulting company based in the U.K., is now developing what it hopes is a game-changing technology dubbed the ‘CryoPower’ engine. “The CryoPower split-cycle engine concept aims to significantly exceed the thermal efficiency of current state-of-the-art heavy-duty diesel engines used in trucks, distributed power systems, and other applications,” said Simon Brewster, CEO Dolphin N2 Ltd, the CryoPower spinoff from Ricardo. “It is based on the use of a separate induction and compression cylinder from the one used for combustion and exhaust, which enables recovery of otherwise wasted exhaust heat to the working gas after the end of compression.”
The compression process is carried out isothermally, cooled via the injection of a small amount of liquid nitrogen. The liquid nitrogen is thus both a coolant and an additional energy vector, which offsets some of the fuel requirement. The combustion process utilizes either renewable or traditional fuels, liquid or gaseous, and delivers heat energy back to the chilled and compressed intake air. Its most important benefit, however, is to enable otherwise unachievable improvements in fuel economy, reduced CO2 and other emissions through improved internal thermal efficiency.
“The addition of liquid nitrogen during the compression stroke reduces the end of compression temperature. The charge air temperature at the end of the compression stroke is then much lower than the exhaust temperature after expansion, enabling recovery of exhaust gas energy to the charge air after compression,” said Brewster. “This heat energy effectively reduces the amount of fuel needed to produce a given level of work and in turn reduces the waste heat energy rejected in the exhaust.”
In practice, the exhaust temperature of a recuperated split-cycle engine is many 100s of degree celsius lesser than a conventional engine. The addition of liquid nitrogen also reduces the work required to compress the charge air to a given pressure and substantially reduced compared to that in a conventional engine cylinder of the same compression ratio.
And since the CryoPower engine does less work compared to a conventional engine, it enjoys a much higher efficiency as losses are reduced. Also for ideal efficiency, a combustion engine requires less compression and more expansion, something that is difficult to achieve with a conventional architecture. The CryoPower concept uses a smaller compression cylinder (or fewer compression cylinders) than its expansion cylinder to make much fuller use of the expansion work.
Enabled by the cooled compression process, exhaust gas heat is transferred from the hot part of the cycle at the end of combustion to the end of compression and before injection of fuel on the next stroke. Transfer of gas between the two cylinders is carried out at high pressure, so the mass flow is high while the volume flow is low. This reduces pumping loss, and the process also has inherently low friction.
“CryoPower is a radically new form of engine. During the past ten years a significant amount of fundamental R&D has gone into developing and de-risking the key processes and systems,” said Brewster. “We are not aware of any direct competitors to the CryoPower concept. During the R&D work over the past decade, we have secured a portfolio of patents covering key areas.”
For the most part, Dolphin N2 does not see any significant challenges in the market, as liquid nitrogen is already used in trucks for functions such as refrigeration, and thus, the development of supply infrastructure would be comparatively inexpensive. “The key attraction for operators would be cost savings, and we would anticipate a payback on the investment in less than one year,” said Brewster.
The team is currently at the stage of moving towards the first multi-cylinder prototype demonstration engine. The investment capital being secured by Dolphin N2 will enable CryoPower to be taken forward to full system demonstration, pilot applications, and industrialization.
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