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Driven by the desire to implement low-cost, high-efficiency NOx aftertreatment systems, such as Three Way Catalysts (TWC) or Lean NOx Traps (LNT), a novel 6-Stroke engine cycle was explored to determine the feasibility of implementing such a cycle on a compression ignition engine while continuing to deliver fuel efficiency. Fundamental questions regarding the abilities and trade-offs of a 6-stroke engine cycle were investigated for near-stoichiometric and lean operation. Experiments were performed on a single-cylinder 15-liter (equivalent) research engine equipped with flexible valvetrain and fuel injection systems to allow direct comparison between 4-stroke and 6-stroke performance across multiple hardware configurations. 1-D engine simulations with predictive combustion models were used to support, iterate on, and explore the 6-stroke operation in conjunction with the experiments.

The Homogeneous Charge Compression Ignition (HCCI) combustion concept is currently under widespread investigation due to its potential to increase thermal efficiency while greatly decreasing harmful exhaust pollutants. Simulation tools have been developed to explore the implications of initial mixture thermodynamic state on engine performance and emissions. In most cases these modeling efforts have coupled a detailed fuel chemistry mechanism with empirical descriptions of the in-cylinder heat transfer processes. The primary objective of this paper is to present a fundamentally based boundary layer heat transfer model. The two-zone combustion model couples an adiabatic core zone with a boundary layer heat transfer model. The model predicts film coefficient, with approximately the same universal shape and magnitudes as an existing global model.

A PC-based, computationally-efficient, quasi-dimensional simulation of HCCI engine performance and emissions has been developed with the intent to bridge the gap between zero-dimensional and sequential fluid-mechanic - thermo-kinetic models. The model couples a detailed chemistry description, a core gas model, a predictive boundary layer model, and a ring-dynamics crevice flow model. The thermal boundary layer, which is axially discretized to account for the relative piston motion, is modeled using compressible energy arguments. The ring-pack crevice zone is modeled using a coupled ring dynamic and flow model. The physically-based mathematical model is solved within the context of a single simulation framework, which lends to flexibility and expediency in performing a range of parametric studies. The simulation was validated under turbo-charged conditions using data obtained from a Caterpillar 3500 test engine.

Natural gas quality, in terms of the volume fraction of higher hydrocarbons, strongly affects the auto-ignition characteristics of the air-fuel mixture, the engine performance and its controllability. The influence of natural gas composition on engine operation has been investigated both experimentally and through chemical kinetic based cycle simulation. A range of two component gas mixtures has been tested with methane as the base fuel. The equivalence ratio (0.3), the compression ratio (19.8), and the engine speed (1000 rpm) were held constant in order to isolate the impact of fuel autoignition chemistry. For each fuel mixture, the start of combustion was phased near top dead center (TDC) and then the inlet mixture temperature was reduced. These experimental results have been utilized as a source of data for the validation of a chemical kinetic based full-cycle simulation.

An experimental investigation of partial premixed charge compression ignition (PCCI) in combination with direct fuel injection was conducted on a Caterpillar C-15 heavy-duty diesel engine (HDDE). The intent of the program was to investigate the performance, emissions, and efficiency characteristics of the concept. A portion of the fuel was delivered to the intake manifold using air-assist port fuel injectors. The spray droplet characteristics were measured, for several different injector geometries, over a range of thermodynamic conditions. Subsequently, the optimized port fuel injector (PFI) was utilized in the engine tests. The engine tests were run at conditions ranging from 1200 - 1800 RPM, loads ranging from 25 - 75%, and PFI quantities ranging from approximately 10 - 70%. The tests showed that oxides of Nitrogen (NOX) emissions did not decrease dramatically with partial premixing.

This paper uses a one-dimensional (1-D) simulation based approach to compare the steady state and transient performance of a Split Cycle Clean Combustion (SCCC) diesel engine to a similarly sized conventional diesel engine. Caterpillar Inc's one-dimensional modeling tool “Dynasty” is used to convert the simulation model of Caterpillar's current production turbocharged diesel engine Cat® C4.4 (used in their Hydraulic Excavator 316) to operate on the SCCC cycle. Steady state and transient engine performance is compared between the two engine variants. This study is focused only on the performance aspects of engine and relies on the other independently published papers for emissions prediction. This paper also demonstrates the use of Caterpillar's proprietary modeling software Dynasty to replicate the two cylinder SCCC engine model presented by University of Pisa in their paper [2].