HCCI update: Prototype in 2008
A couple months ago, Bruno pointed AutoblogGreen readers to a New York Times article summarizing the current status of Homogeneous Charge Compression Ignition (HCCI) engines, technology that attempts to take the best of both diesels and gasoline-fueled internal combustion engines. This Engineer Online article introduces us to Dr. Zhijun Peng, a professor in the engineering department at Sussex University, who is also working on bringing HCCI to the real world.Peng's project was awarded £200,000 (about $377,350) for 27 months of research on HCCI technology. Both Caterpillar and BP are backing the project while additional funding will be provided by the U.K.'s Department of Trade and Industry (DTI).
Peng expects to have a working prototype by the end of 2008, however, he summarizes HCCI's current obstacles as three-fold:
- Providing the right temperature and pressure for combustion
- Achieving a high load while avoiding knocking
- Determining the best way to start the engine, especially from cold.
[Source: The Engineer Online]
Reader Comments (Page 1 of 1)
Mike 10:06AM (9/15/2006)
This is good news for emissions. With homogeneous combustion, there are few particulates and with significantly lower peak temperatures, oxides of nitrogen levels are negligible.
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Pao Chi Pien 11:23AM (12/11/2006)
Fuel/air mixture temperature can be increase by compression or chemical kinetics. Because temperature increase by compression can be more accurately controlled than by chemical kinetics, the compression temperature should be utilized to initial the autoignition of the homogeneous charge. Temperature contribution from chemical kinetics can be greatly reduced by having a two-stroke engine configuration where the time available for chemical kinetics is drastically reduced. Furthermore, HCCI engine power density is greatly increased by double the number of power strokes at same engine rpm. This concept is fully described in Patent No.: US 7,114,485 B2 issued on Oct. 3, 2006.
A new two-stroke engine to operate on overexpanded two-stroke HCCI cycle may be obtained by contacting me.
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Pao Chi Pien 7:25PM (8/30/2007)
Dear Dr. Peng,
I am aware of your work in the field of HCCI combustion and engine development. I have taken an alternative approach to achieving the benefits of HCCI combustion while addressing the challenge of controlling the timing of HCCI combustion over the full range of operating conditions required for commercial application.
When homogeneous charge reaches a flashpoint by compression or chemical kinetics, autoignition combustion will takes place. With autoignition combustion of the homogeneous fuel/air mixture, the whole mixture burns simultaneously and no product of combustion is compressed to a higher temperature and thus there is no post combustion temperature gradient. Because chemical kinetics temperature increase is extremely difficult to control, my new approach utilizes an appropriate variable compression ratio value (depend on engine loading and rpm) to reach a temperature very close to but slightly below the flashpoint of the homogenous mixture and use spark ignition to initiate HCCI-like combustion. This spark initiated combustion achieves the same benefits of homogeneous charge autoignition combustion.
I have created a two-stroke homogeneous charge spark-ignition (HCSI) engine, which relies on variable valve actuation to vary the compression ratio. The thermal efficiency of a reciprocating engine is a function of the expansion ratio rather than the compression ratio. Therefore, I choose a large expansion ratio first for achieving high thermal efficiency at all-loads.
It is known that the autoignition temperature of hydrocarbon fuel is between 900° – 1000°K. Because of my two-stroke engine configuration, a very short duration of the homogeneous charge in the cylinder (for pre-combustion chemical kinetic interaction), I choose a compression ratio of 14.5 to give a compression temperature of 906.4°K at the end of the compression process. To start a two-stroke HCSI engine and to run at low loads, a compression ratio of 14.5 not only provides the required compression temperature, but also obtains high enough compression pressure such that the exhaust pressure at the end of expansion process is higher than the atmospheric pressure.
For high loads, the variable compression ratio is switched from 14.5 to a sufficiently low value to prevent pre-ignition. Even though this lower compression ratio means that a lower volume of homogeneous charge is admitted to the cylinder, fuel injection per cycle is increased to meet the power demand. Because of the compression temperature is far below the flashpoint of the mixture, there is a large post combustion temperature gradient. High temperature NOx (but no other emissions) will be produced.
I would welcome your thoughts on this new approach.
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