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The effects of port fuel injection (PFI) timing and targeting on air/fuel (A/F) control, exhaust emissions, and combustion stability at retarded spark timing were investigated on a 2.0L I-4 engine with production injectors (300-350 micron SMD droplet spray). Timings were fully closed valve injection (CVI) or fully open valve injection (OVI), and selected targetings were towards the valve or port floor. An “ideal” pre-vaporized, pre-mixed fuel system was also tested to provide a baseline with which to isolate PFI fuel preparation effects. The key findings were: Transient A/F excursions with PFI were minimized over the full temperature range with OVI timing and valve targeting. The X-tau modeled film mass for OVI/valve target was 50% less than CVI/valve target and 30% less than OVI/port target with a cold engine (20° C). When fully warm (90° C), the A/F response of CVI/valve target improved to near that of OVI.

Spark retard is desirable for decreasing cold start hydrocarbon emissions and lighting off the catalyst more rapidly. The focus of this work is to better understand the nature of the HC emissions as spark is retarded and investigate the location of the oxidation (in-cylinder or in the exhaust port and manifold). Fast FID measurements were taken in the exhaust port of a single cylinder research engine during cold, retarded spark engine operation (1200 rpm, 2.5 bar IMEP, 20 °C fluids). At moderate spark retard both Fast FID (exhaust port) and exhaust plenum HC levels decreased due to reduced crevice volume fraction at the end of burn, and increased in-cylinder burn up. In contrast, at large spark retard the port HC's increased dramatically while the exhaust plenum levels continued to fall to near zero. This is thought to be due to the onset of incomplete in-cylinder combustion along with increased exhaust port and manifold after-burning caused by the increasing exhaust gas temperatures.

Engine operation with spark ignition retarded from MBT timing is used at cold start to reduce HC emissions and increase exhaust gas temperature; however it also results in increased cyclic variations. Steady-state cold fluids testing was performed to better understand the causes of the cycle-to-cycle variations. Detailed analysis of individual cycles was performed to help gain an understanding of the causes of cyclic variations. The important results were: The primary cause of cyclic variations in IMEP is variations in the combustion phasing (location of 50% mass fraction burned). The expansion ratio decreases rapidly during combustion for retarded spark timing and therefore the phasing determines individual cycle thermal efficiency and IMEP. Variations in the late burn have little impact on the IMEP as this combustion occurs close to EVO and does little expansion work.

A steady-state flowbench measures the mass and angular momentum flux (swirl and tumble) for a given cylinder head intake port design over varying valve lifts and pressure drops. From these two measurements, enhancements in volumetric efficiency and burnrate can be determined. This methodology, however, requires the production and experimental testing of multiple cylinder head castings or soft-prototypes. To help reduce the number of hardware design iterations, an analytical methodology has been developed which uses a new computational fluid dynamics (CFD) simulation tools called PowerFLOW. From a solid model of the cylinder head, PowerFLOW uses automeshing which produces a 10 million Cartesian volume mesh in 4 CPU hrs. The lattice Boltzmann technique used by PowerFLOW is inherently parallel resulting in steady-state results on this mesh in 36 CPU hrs. This paper present a comparison of numerically obtained mass flow rates from PowerFLOW to experimental flowbench data.

Using a fast-sampling valve, residual-fraction levels were determined in a 2.0L spark-ignited production engine, over varying engine operating conditions. Individual samples for each operating condition were analyzed by gas-chromatography which allowed for the determination of in-cylinder CO and CO2 levels. Through a comparison of in-cylinder measurement and exhaust data measurements, residual molar fraction (RMF) levels were determined and compared to analytical results. Analytical calculations were performed using the General Engine SIMulation (GESIM) which is a steady state quasi-dimensional engine combustion cycle simulation. Analytical RMF levels, for identical engine operating conditions, were compared to the experimental results as well as a sensitivity study on wave-dynamics and heat transfer on the analytically predicted RMF. Similarly, theoretical and experimental NOx emissions were compared and production sensitivity on RMF levels explored.

This study was performed to quantify the effects of injector targeting and fuel volatility on transient A/F excursions and fuel film mass in a port fuel injected (PFI) engine. Two injector targeting positions as well as injection timing and four different fuels were studied. Warm-up tests were performed with the throttle ramped between two positions over a one second interval to provide smooth changes in airflow and injected fuel. The exhaust A/F was recorded for each transient and fit using the X-τ model to estimate the change in the liquid fuel stored in the port and cylinder due to the throttle ramp. The change in fuel stored in the films was: ∼20% less with valve targeting ∼30% less with IVO injection timing 50-100% higher for hesitation fuel

A single-cylinder, two-valve engine was operated with independent cooling circuits for the engine block and cylinder head to investigate the effect of temperature distribution on HC emissions. The goal was to understand and quantify the mechanisms responsible for decreased HC emissions at elevated temperatures. Tests were run at a typical road load condition using two different fuels (a 97 RON blend and isopentane - to eliminate liquid fuel and oil layer absorption effects). The total HC emissions (97 RON fuel) decreased by 15-20% with an increase in either the cylinder head or engine block coolant temperature from 71 to 110 °C. When operating with isopentane the HC emissions decreased by 15-20% with an increase in the engine block temperature from 71 to 110 °C but were essentially unaffected by cylinder head temperature. This indicates that the cylinder head temperature primarily influenced the HC emissions from liquid fuel effects.

New regulations from the state of California have established, for the first time, reactivity-based exhaust emissions standards for new vehicles and require that any clean alternative fuels needed by these vehicles be made available. Contained in these regulations are provisions for “reactivity adjustment factors” which will provide credit for vehicles which run on reformulated gasoline. The question arises: given two fuels of different chemical composition, but both meeting the criteria for CA Phase 2 gasoline (reformulated gasoline), how different might the specific reactivity of the exhaust hydrocarbons be? In this study we explored this question by examining the engine-out HC emissions from a single-cylinder version of the 5.4 L modular truck engine run on two different CA Phase 2 fuels.