Heat Release Design Method for HCCI in Diesel Engines with Simulation 2008-28-0006
A simple thermodynamically based engine design tool is developed to allow engine designers to start with the engine peak pressure limit, desired IMEP, and constraints on rate of pressure rise and thus generate an idealized Wire-Frame cylinder pressure cycle. After conversion into crank-angle based pressures, the apparent heat release rate (AHRR) is generated. The resulting AHRR1 represents an idealized heat release rate which is required to achieve the engine performance goals. This target AHRR is thus known prior to engine testing and serves as a guide to HCCI combustion test engineers.
Using the Wire-Frame cycle tool, the ideal heat release rate for HCCI combustion is identified. For low IMEP, this is a single mode HRR centered at TDC. However, for medium and high loads, the combustion must be modified.
Based upon the indications of the Wire-Frame HRR design tool, a few methods are identified and explored which allow higher IMEP from HCCI type combustion. Reducing the engine compression ratio and slowing the rate of combustion are practical means to increase the IMEP from single mode HCCI combustion, however, with an efficiency penalty.
Analysis of results from the model indicate that achieving full load IMEP in a practical engine may require the development of a two-stage combustion process, with HCCI serving the first stage. The best option for increasing IMEP while using an HCCI type heat release is to delay the onset of heat release. This retains HCCI like HRR with only moderate loss of efficiency.
Additional analysis was carried out using the 1D gas dynamics code GT-Power to test the validity of four of the operating conditions. These results demonstrated that the Wire-Frame cycle tool characterizes and bounds the behavior of a high-fidelity simulation. Application of these tools creates the requirements that will flow down to hardware designers, and minimize the amount of guesswork needed to optimize combustion system design.