Low Temperature Combustion with Thermo-Chemical Recuperation 2007-01-4074
The key to overcoming Low Temperature Combustion (LTC) load range limitations is based on suitable control over the thermo-chemical properties of the in-cylinder charge. The proposed alternative to achieve the required control of LTC is the use of two separate fuel streams to regulate timing and heat release at specific operational points, where the secondary fuel, with different autoignition characteristics, is a reformed product of the primary fuel in the tank. It is proposed in this paper that the secondary fuel is produced using Thermo-Chemical Recuperation (TCR) with steam/fuel reforming. The steam/fuel mixture is heated by sensible heat from the engine exhaust gases in the recuperative reformer, where the original hydrocarbon reacts with water to form a hydrogen rich gas mixture. An equilibrium model developed by Gas Technology Institute (GTI) for n-heptane steam reforming was applied to estimate reformed fuel composition at different reforming temperatures. Laboratory results, at a steam/n-heptane mole ratio less than 2:1, confirm that reforming reactions, in the temperature range of 550 K to 650 K, can produce 10-30% hydrogen (by volume, wet) in the product stream.
Also, the effect of trading low mean effective pressure for displacement to achieve high power output and energy efficiency has been explored by WVU. In this feasibility study, a zero-dimensional model of LTC using n-heptane as fuel and a diesel Compression Ignition (CI) combustion model were employed to estimate pressure, temperature and total heat transfer as inputs for a mechanical and thermal losses model. Model results showed that the total cooling burden on a LTC engine with higher displacement and lower power density was 15.6% lower than the diesel engine for the same amount of energy addition in the case of high load (43.57 mg fuel/cycle). These preliminary modeling and experimental results suggest that the LTC-TCR combination may offer a high efficiency solution to engine operation at a time when emissions regulations are causing diesel engines and aftertreatment systems to become more complex.