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In-cylinder pre-processing (or recompression reaction) of direct-injected fuel during the negative valve overlap period of a retention-strategy HCCI engine is investigated for extension of the low-load limit of operation. Experimental studies of three variables (compression ratio, pilot injection timing, and pilot injection amount) were conducted in order to optimize the effects of recompression reaction by changing the sensible and chemical energy environment during recompression. The results from compression ratio variation show that there exist optimum values of equivalence ratio and extent of recompression reaction, which expand the low-load operating region. The pilot injection timing variation demonstrates good controllability of the extent of recompression reaction by effectively changing the in-cylinder residence time of the pilot-injected fuel.

Residual-effected HCCI is investigated using a single-cylinder research engine equipped with fully-flexible variable valve actuation. Dilution limits are explored with various valve profiles in order to gain insight into the best way to use exhaust residual to achieve and control HCCI. The tests repeatedly point out the importance of delayed combustion phasing to reduce thermal losses and maximize efficiency. Combustion phasing is not significantly affected by charge in-cylinder residence time, but is strongly influenced by both the level of exhaust residual and by valve strategies that aim to affect homogeneity. Further dilution with air shows little promise for reaching lower loads, but does suggest that operation near the lean limit can maximize efficiency while minimizing NO and CO emissions.

Studies have been conducted to assess the potential of variable valve actuation to initiate homogeneous charge compression ignition (HCCI) through reinduction of exhaust from the previous combustion cycle. As opposed to strategies which induce HCCI through use of either intake or exhaust throttling, use of exhaust reinduction incurs no pumping penalty, making it particularly attractive as a method for achieving efficient, light-load combustion. Using a fully flexible electrohydraulic valve actuation system, tests were conducted on a single-cylinder research engine using three strategies: late exhaust valve closing, late intake valve opening (used in conjunction with the exhaust valve being left open throughout the intake stroke), and a combination of the two. Results show that IMEP values from ∼30-55% of unthrottled SI combustion output could be obtained by varying the valve timings used to implement reinduction.

In this paper we present photographic and pressure data that describe the autoignition and combustion processes of transient fuel sprays under diesel-like conditions. The results were obtained in a constant-volume vessel that allowed complete optical access to the diesel spray ignition/combustion process. The combination of complete optical access and schlieren/luminosity visualization presents a unique view of the spray. From the data, a narrative of the features of diesel spray autoignition and combustion is constructed. Comparison of events at different gas-phase temperatures shows the effect of shifting the chemical induction time relative to the fluid mechanic transport time. The data show that a key feature of the autoignition process is the formation and shedding of fuel eddies along the edges of the spray jet. These eddies provide an environment conducive to chemical reaction, without the disruptive effects of the spray core fluid mechanics.

Methanol and ethanol are being considered as alternative fuels for diesel engines. One of the key concerns with using alcohol fuels in diesel engines is their poor ignition quality. This work presents the ignition characteristics of methanol and ethanol examined under simulated diesel engine conditions in a constant-volume combustion vessel. The ignition characteristics of isooctane and normal hexadecane (cetane) measured under the same conditions are also included for reference. Results show that to obtain ignition delays and rates-of-pressure-rise suitable for current diesel engine designs, methanol and ethanol require in-cylinder temperatures of about 1100 K at the time of injection. The results also show that the ignition delays of the alcohol fuels are independent of the chamber pressure and are unaffected by the presence of 10% by volume of water in the fuel.

A photographic study was conducted using an optical-access compression-expansion machine in order to reveal the mechanism of ignition and flame propagation initiated by plasma igniters. The tests included a jet igniter with inert cavity liner (quartz), a jet igniter with reactive cavity liner (paraffin), and a J-gap spark plug. Schlieren cinematographic records were obtained for each condition along with concomitant pressure traces. Basic features of ignition and combustion at lean limit were determined for each igniter. The spark plug permited lean operation down to an equivalence ratio of 0.7, after which mis-ignition occurred. Jet igniters provided an extension of lean limit to 0.5 in equivalence ratio. For jet igniters, these limits were imposed by either extinction of the flame or too slow burning rate, rather than by misfire.

Performance of an array of plasma ignition systems has been studied in a CFR engine.This included a standard spark plug, an extended spark plug, a surface discharge plug, and two plasma jet ignitors, one with open cavity and the other with cavity provided with a jet forming orifice.For all the tests the engine was run at a compression ratio of 3:1, a wide open throttle, and minimum for best torque (MBT) ignition timing. In this way specific information was obtained on ignition delay, duration of the exothermic combustion process, engine efficiency, and pollutant emissions.The study demonstrated the effect of various ignition systems on engine performance as the lean operating limit is approached.

Three 1978 Ford Pinto 2300 cc vehicles were retrofitted to operate on neat methanol and driven for an 18-month period. The modification package included carburetor rejetting, upgraded fuel filtration and electric cold start assistance. Internal engine components (excepting camshafts) and the engine lubrication system were not modified. A conventional motor oil was used in all vehicles. Over 30,000 vehicle miles were accumulated in the test period. Wear metal samples were taken at 1000-mile intervals and analyzed for 16 metallic constituents using Direct Reading Emission Spectroscopy (DRES). Percentage fuel and water dilution were also measured. All oil samples showed abnormally high concentrations of lead and tin. Iron accumulation rates over the entire test were similar to those reported for gasoline engines. Maximum fuel or water dilution in any sample was 0.5%.

Alcohols (both ethanol and methanol) have been recognized as alternative fuels to replace dwindling gasoline supplies. In previous studies, the alcohols have shown a potential for lowering the emissions of regulated species (hydrocarbons, carbon monoxide, oxides of nitrogen.) In order to assess three-way catalyst performance on alcohol fuels, three 1978 Ford Pintos have been retrofitted to run on neat methanol, fuel. Over 30,000 vehicle miles have been assumulated during an 18-month period. Driveability, fuel economy and emission histories (CVS-78) have been obtained. Regulated emissions levels of all vehicles were below 1983 United States Federal standards throughout 10,000 miles of operation on each vehicle. Aldehyde emissions were a factor of three higher for methanol operation than gasoline. The energy economies for highway and urban driving cycles on the two fuels were comparable. Catalytic system efficiency for both fuels were evaluated.