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The objective of this research is a detailed investigation of multiple injections in a highly-dilute diesel low temperature combustion (LTC) regime. This research concentrates on understanding the performance and emissions benefits of multiple injections via experiments and simulations in a 0.48L signal cylinder light-duty engine operating at 2000 r/min and 5.5 bar IMEP. Controlled experiments in the single-cylinder engine are then combined with three computational tools, namely heat release analysis of measured cylinder pressure, a phenomenological spray model using in-cylinder thermodynamics [1], and KIVA-3V Chemkin CFD computations recently tested at LTC conditions [2]. This study examines the effects of fuel split distribution, injection event timing, rail pressure, and boost pressure which are each explored within a defined operation range in LTC.

The objective of this research is a detailed investigation of unburned hydrocarbon (UHC) in a highly-dilute diesel low temperature combustion (LTC) regime. This research concentrates on understanding the mechanisms that control the formation of UHC via experiments and simulations in a 0.48L signal-cylinder light duty engine operating at 2000 r/min and 5.5 bar IMEP with multiple injections. A multi-gas FTIR along with other gas and smoke emissions instruments are used to measure exhaust UHC species and other emissions. Controlled experiments in the single-cylinder engine are then combined with three computational tools, namely heat release analysis of measured cylinder pressure, analysis of spray trajectory with a phenomenological spray model using in-cylinder thermodynamics [1], and KIVA-3V Chemkin CFD computations recently tested at LTC conditions [2].

The effects of varying nozzle spray angle and rail pressure on emissions and thermal efficiency each were explored using a 103-mm bore direct-injection single-cylinder diesel engine. Spray angles from 120° to 158° significantly changed the spray targeting within the 16:1 compression ratio reentrant-shaped piston bowl. At one part load operating condition injection timing was varied over a range of 15° to 30° btc to investigate pre-mixed compression ignition (PCI) combustion with 800 bar rail pressure while varying EGR to maintain a constant low NOx emission index of 0.4 g/kg. The observed trends are explained by the combined effects of spray angle and injection timing and, in particular, the calculated amount of liquid spray that misses the piston bowl is directly linked to the measured increases in HC, CO, and smoke emissions and a reduction in thermal efficiency.

There is a significant global effort to study low temperature combustion (LTC) as a tool to achieve stringent emission standards with future light duty diesel engines. LTC utilizes high levels of dilution (i.e., EGR > 60% with <10%O2 in the intake charge) to reduce overall combustion temperatures and to lengthen ignition delay, This increased ignition delay provides time for fuel evaporation and reduces in-homogeneities in the reactant mixture, thus reducing NOx formation from local temperature spikes and soot formation from locally rich mixtures. However, as dilution is increased to the limits, HC and CO can significantly increase. Recent research suggests that CO emissions during LTC result from the incomplete combustion of under-mixed fuel and charge gas occurring after the premixed burn period [1, 2]1. The objective of the present work was to increase understanding of the HC/CO emission mechanisms in LTC at part-load.

A phenomenological engine model has been developed to study direct injection of liquid fuels in diesel and gasoline engines. Sub-models were obtained from the literature wherever possible and include those for initial drop size, droplet vaporization, and spray penetration. The progress of the injected spray, including both liquid and vapor, is visualized relative to the combustion chamber bowl boundaries and gives valuable insight on where the spray tip intersects the piston bowl surface, and whether it is in a liquid or gaseous state. The one-dimensional spray penetration used in the model is oblivious to surfaces (thus no spray-wall interactions), air motion, turbulence, and mixing with air, but is properly influenced by gas temperature and density.

Simultaneous reduction of nitric oxides (NOx) and particulate matter (PM) emissions is possible in a diesel engine by employing a Partially Premixed Compression Ignition (PPCI) strategy. PPCI combustion is attainable with advanced injection timings and heavy exhaust gas recirculation rates. However, over-advanced injection timing can result in the fuel spray missing the combustion bowl, thus dramatically elevating PM emissions. The present study investigates whether the use of narrow spray cone angle injector nozzles can extend the limits of early injection timings, allowing for PPCI combustion realization. It is shown that a low flow rate, 60-degree spray cone angle injector nozzle, along with optimized EGR rate and split injection strategy, can reduce engine-out NOx by 82% and PM by 39%, at the expense of a modest increase (4.5%) in fuel consumption.

The Representative Interactive Flamelet (RIF) - model has established itself as a model well suited for capturing conventional non-premixed combustion in diesel engines. There are concerns about applying the concept to model combustion modes characterized by high degrees of premixing, since it is argued that the fast-chemistry assumption, on which the model is based, breaks down. However, the level of premixing at which this occurs is still not well established. In this paper the model is successfully applied to the so-called Premixed Charge Compression Ignition (PCCI) mode of combustion, characterized by relatively early injection timings, high EGR, and cooled intake air. For very advanced injection timings, an alternative modeling approach is developed.

Secondary air scheduling and average delivery rate have a great influence on the performance (carbon monoxide and hydrocarbon cleanup) of rich thermal manifold reactors. A continuously modulated secondary air system was devised to provide a tailpipe air-fuel ratio that did not change significantly with engine speed or load when a “flat” carburetion calibration was incorporated. This system involved throttling the inlet of the air pump(s) so that the air pump and engine intake pressures were equal. The continuous air modulation system was compared with an unmodulated system and a step-modulated system. The secondary air systems were investigated with both GMR “small volume” cast iron thermal reactors and Du Pont V thermal reactors on modified 350 CID V-8 engines in 1969 Chevrolet passenger vehicles. It was found that thermal reactor performance improved with each increase in control of the secondary air schedule.

A staged combustion engine has been evaluated in which pairs of cylinders are coupled in series. The first cylinder of the pair inducts and burns a homogeneous, fuel-rich mixture which produces exhaust products containing substantial amounts of combustibles (CO, H2, and HC) and only small quantities of NOX. These products are then cooled, mixed with additional air, and inducted into another cylinder for a second stage of combustion. Additional work is extracted in this second stage, where substantial cleanup of CO and HC occurs while maintaining a low level of NOX. Experiments with a two-cylinder research engine showed that low NOX emission could be obtained without sacrificing engine efficiency. However, approximately 40 percent more displacement is required to produce the same power as conventional SI engines. The sources of HC, CO, and NOX emissions were investigated, as were the effects of major engine variables on these exhaust emissions and fuel consumption.

The concept of the variable stroke engine (VSE) is explained and the problems related to its use are discussed. Single cylinder combustion data are combined with published multi-cylinder VSE friction data to formulate engine model. This engine model is coupled with a vehicle model to make projections of 55/45 fuel economy and NOx g/mile which are compared with similar projections for a throttled engine. At an NOx level of 0.93 g/km (1.5 g/mile), VSE fuel economy improvements ranged from 2 to 20%, depending upon the frictional losses and vehicle power-to-weight ratio used in the models.

The effect of bore-to-stroke ratio (B/S) on indicated specific fuel consumption (ISFC) and emissions of a gasoline-fueled, spark-ignited, single-cylinder engine was studied while holding compression ratio and bore diameter constant. As B/S was increased from 1.1 to 3.3, both ISFC and hydrocarbon emissions increased significantly. Increased cylinder heat loss and, to a lesser extent, increased combustion duration were the principal causes of the ISFC increase. Increased surface-to-volume ratio was the principal cause of the increase in hydrocarbon emissions. The influence of combustion chamber modifications on these effects was investigated.