The closed-cycle hydrogen-fueled argon power cycle is a zero emissions concept
that combines a carbon-free fuel with argon as a diluent replacement for
nitrogen. The lack of nitrogen in the argon power cycle results in zero NOx
emissions on an internal combustion engine platform. There is also massive
efficiency improvement because argon is monatomic and has a very high ratio of
specific heats. However, this will also result in combustion temperatures and
pressures exceeding those normally achieved on an air-standard engine platform.
The literature shows conflict between modeling, which promises incredibly high
efficiency gains, and experiment, which show more modest efficiency gains.
This work combined thermodynamic modeling, literature analysis, and experiments
to understand this discrepancy and ultimately understand what level of
efficiency gain can be expected for the argon power cycle. It was found that
while low compression ratio engines stand to see the largest relative efficiency
improvement, high compression ratio engines are the ones that can ultimately
achieve ~60%+ efficiency, corresponding to a 15–20% relative improvement in
efficiency over an air-standard engine platform operating at or above 50%
efficiency. The elevated temperatures and pressures of the cycle result in knock
in spark ignition, so either a high compression ratio knock mitigation strategy
or mixing-controlled operation is required. Experiments conducted using a
diesel-fueled compression ignition engine showed that a 30% argon replacement
resulted in ~6% and full nitrogen replacement with argon resulted in ~14%
relative efficiency improvement at 8 bar gross indicated mean effective pressure
(IMEPg) without intake boosting on a heavy-duty engine with a compression ratio
of 20.0 and late intake valve closing, agreeing with modeling results. The key
takeaway to match modeling and experimental trends is to accurately model heat
transfer, which increases significantly for the argon power cycle.