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Technical Paper

Thermodynamic Advantages of Low Temperature Combustion (LTC) Engines Using Low Heat Rejection (LHR) Concepts

Low temperature combustion (LTC) modes for reciprocating engines have been demonstrated with relatively high thermal efficiencies. These new combustion modes involve various combinations of stratification, lean mixtures, high levels of exhaust gas recirculation (EGR), multiple injections, variable valve timings, two fuels, and other such features. LTC engines may be attractive in combination with low heat rejection (LHR) engine concepts. The current work is aimed at evaluating the thermodynamic advantages of such a LTC-LHR engine. A thermodynamic cycle simulation was used to evaluate the effect of cylinder wall temperature on the engine performance, emissions and second law characteristics. An automotive engine at 2000 rpm with a bmep of 900 kPa was considered. Both a conventional and a LTC design were compared. The LTC engine realized small gains in efficiency whereas the conventional engine did not realize any significant gains as the cylinder wall temperature was increased.
Journal Article

A Thermodynamic Evaluation of the Use of Alcohol Fuels in a Spark-Ignition Engine

Although the use of alcohol fuels in spark-ignition engines has been investigated for over 100 years, consistent and thorough thermodynamic evaluations are few. The current work examines the detail thermodynamics of the use of methanol and ethanol by an automotive, spark-ignition engine. Overall engine performance parameters, detail instantaneous quantities, and second law parameters are determined as functions of engine design and operating conditions. In addition, the results for the alcohol fuels are compared to results for isooctane. Results include indicated and brake efficiencies, heat transfer, and exhaust gas temperatures as functions of engine speed and load. Operating conditions include constant equivalence ratio (stoichiometric), MBT spark timing, and constant burn duration. In general, the thermodynamic results are similar for the alcohol fuels and isooctane.
Technical Paper

Results from a Thermodynamic Cycle Simulation for a Range of Inlet Oxygen Concentrations Using Either EGR or Oxygen Enriched Air for a Spark-Ignition Engine

An engine cycle simulation which included the second law of thermodynamics was used to examine the engine performance and the thermodynamic characteristics of a spark ignition engine as functions of the oxygen inlet concentration. A wide range of oxygen inlet concentrations (12% to 40% by volume) was considered. For oxygen inlet concentrations less than 21%(v), EGR was used, and for oxygen inlet concentrations greater than 21%(v), oxygen enriched inlet air was used. Two EGR configurations were considered: (1) cooled and (2) adiabatic. In general, engine efficiencies decreased, heat transfer increased, nitric oxide emissions increased, and the destruction of availability (exergy) decreased as the oxygen concentration increased.
Technical Paper

A Cycle Simulation Including the Second Law of Thermodynamics for a Spark-Ignition Engine: Implications of the Use of Multiple-Zones for Combustion

A thermodynamic cycle simulation using multiple zones for the combustion process was used to obtain the performance, energy and availability characteristics for an automotive spark-ignition engine. In addition to the traditional formulations based on the first law of thermodynamics, the simulation also included considerations based on the second law of thermodynamics. The characteristics of the engine combustion process and the impact of the multiple-zone formulation were determined. The burned gases were divided into an adiabatic core and boundary layer. The heat transfer of the burned gases was assigned in total to the boundary layer. From the start of combustion until 90°aTDC, the difference between the temperatures of the adiabatic core and the burned gases increased from zero to about 250 K. The implications of this temperature increase on nitric oxide computations are discussed.
Technical Paper

A Review of Investigations Using the Second Law of Thermodynamics to Study Internal-Combustion Engines

Investigations that have used the second law of thermodynamics to study internal-combustion engines in a detailed manner date back to the late 1950s. Over two dozen previous investigations which have used the second law of thermodynamics or availability analyses were identified. About two-thirds of these have been completed for diesel engines, and the other one-third have been completed for spark-ignition engines. The majority of these investigations have been completed since the 1980s. A brief description of each of these investigations is provided. In addition, representative results are presented for both compression-ignition (diesel) and spark-ignition engines to illustrate the type of information obtained by the use of second law analyses. Both instantaneous values for the engine availability, and the overall values for energy and availability are described.
Technical Paper

Operating Characteristics of a Spark-Ignition Engine Using the Second Law of Thermodynamics: Effects of Speed and Load

A thermodynamic cycle simulation was used to obtain the performance, energy and availability characteristics as functions of speed and load for an automotive spark-ignition engine. Availability is an important thermodynamic property related to the second law of thermodynamics. The manner in which the total original energy and availability are used, displaced or destroyed is exhibited. As an example of the results, the availability destroyed by the combustion process (as a percentage of the fuel availability) ranged between 20.3 and 21.4%. This fraction was lowest for the highest speeds and loads, since these conditions were best at preserving the fuel availability.