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An experimental study was performed to develop a more fundamental understanding of the effects of secondary air injection (SAI) on exhaust gas emissions and catalyst light-off characteristics during cold start of a modern SI engine. The effects of engine operating parameters and various secondary air injection strategies such as spark retardation, fuel enrichment, secondary air injection location and air flow rate were investigated to understand the mixing, heat loss, and thermal and catalytic oxidation processes associated with SAI. Time-resolved HC, CO and CO₂ concentrations were tracked from the cylinder exit to the catalytic converter outlet and converted to time-resolved mass emissions by applying an instantaneous exhaust mass flow rate model. A phenomenological model of exhaust heat transfer combined with the gas composition analysis was also developed to define the thermal and chemical energy state of the exhaust gas with SAI.

The rotary engine provides high power density compared to piston engine, but one of its downside is higher oil consumption. In order to better understand oil transport, a laser induced fluorescence technique is used to visualize oil motion on the side of the rotor during engine operation. Oil transport from both metered oil and internal oil is observed. Starting from inside, oil accumulates in the rotor land during inward motion of the rotor created by its eccentric motion. Oil seals are then scraping the oil outward due to seal-housing clearance asymmetry between inward and outward motion. Cut-off seal does not provide an additional barrier to internal oil consumption. Internal oil then mixes with metered oil brought to the side of the rotor by gas leakage. Oil is finally pushed outward by centrifugal force, passes the side seals, and is thrown off in the combustion chamber.

Diffusive combustion of direct injected ethanol is investigated in a heavy-duty single cylinder engine for a broad range of operating conditions. Ethanol has a high potential as fossil fuel alternative, as it provides a better carbon footprint and has more sustainable production pathways. The introduction of ethanol as fuel for heavy-duty compression-ignition engines can contribute to decarbonize the transport sector within a short time frame. Given the resistance to autoignition of ethanol, the engine is equipped with two injectors mounted in the same combustion chamber, allowing the simultaneous and independent actuation of the main injection of pure ethanol and a pilot injection of diesel as an ignition source. The influence of the dual-fuel injection strategy on ethanol ignition, combustion characteristics, engine performance and NOx emissions is evaluated by varying the start of injection of both fuels and the ethanol-diesel ratio.

Diesel engine manufacturers strive towards further efficiency improvements. Thus, reducing in-cylinder heat losses is becoming increasingly important. Understanding how location, thermal insulation, and engine operating conditions affect the heat transfer to the combustion chamber walls is fundamental for the future reduction of in-cylinder heat losses. This study investigates the effect of a 1mm-thick plasma-sprayed yttria-stabilized zirconia (YSZ) coating on a piston. Such a coated piston and a similar steel piston are compared to each other based on experimental data for the heat release, the heat transfer rate to the oil in the piston cooling gallery, the local instantaneous surface temperature, and the local instantaneous surface heat flux. The surface temperature was measured for different crank angle positions using phosphor thermometry.

Inorganic engine lubricant additives, which have various specific, necessary functions such as anti-wear, leave the combustion chamber bound to soot particles (approximately ≤1% by mass) as ash [13], and accumulate in aftertreatment components. The diesel particulate filter (DPF) is especially susceptible to ash-related issues due to its wall-flow architecture which physically traps most of the soot and ash emissions. Accumulated lubricant-derived ash results in numerous problems including increased filter pressure drop and decreased catalytic functionality. While much progress has been made to understand the macroscopic details and effects of ash accumulation on DPF performance, this study explores the nano- and micron-scale forces which impact particle adhesion and mobility within the particulate filter.

Particulate emissions from a production gasoline direct injection spark ignition engine were studied under a typical cold-fast-idle condition (1200 rpm, 2 bar NIMEP). The particle number (PN) density in the 22 to 365 nm range was measured as a function of the injection timing with single pulse injection and with split injection. Very low PN emissions were observed when injection took place in the mid intake stroke because of the fast fuel evaporation and mixing processes which were facilitated by the high turbulent kinetic energy created by the intake charge motion. Under these conditions, substantial liquid fuel film formation on the combustion chamber surfaces was avoided. PN emissions increased when injection took place in the compression stroke, and increased substantially when the fuel spray hit the piston.

A dynamometer-mounted four-cylinder Saturn engine was used to accumulate combustion chamber deposits (CCD), using an additized fuel. During each deposit accumulation test, the HC emissions were continuously measured. The deposit thickness at the center of the piston was measured at the beginning of each day. After the 50 and 35-hour tests, HC emissions were measured with isooctane, benzene, toluene, and xylene, with the deposited engine, and again after the deposits had been cleaned from the engine. The HC emissions showed a rapid rise in the first 10 to 15 hours and stabilization after about 25 hours of deposit accumulation. The HC increase due to CCD accumulation accounted for 10 to 20% of the total engine-out HC emissions from the deposit build-up fuel and 10 to 30% from benzene, isooctane, toluene, and xylene, making CCDs a significant HC emissions source from this engine. The HC emissions stabilized long before the deposit thickness.

The characteristics of the early development of fuel sprays from pressure swirl atomizer injectors of the type used in direct injection gasoline engines is investigated. Planar laser-induced fluorescence (PLIF) was used to visualize the fuel distribution inside a firing optical engine. The early spray development of three different injectors at three different fuel pressures (3, 5, and 7 MPa) was followed as a function of time in 30 μsec intervals. Four phases could be identified: 1) A delay phase between the rising edge of the injection pulse and the first occurrence of fuel in the combustion chamber, 2) A solid jet or pre-spray phase, in which a poorly atomized stream of liquid fuel during the first 150 μsec of the injection. 3) A wide hollow cone phase, separation of the liquid jet into a hollow cone spray once sufficient tangential velocity has been established and 4) A fully developed spray, in which the spray cone angle is narrowed due to a low pressure zone at the center.

Experiments were carried out to collect in-cylinder pressure data and microphone signals from a single-cylinder test engine using spark timingsbefore, at, and after knock onset for toluene reference fuels. The objective was to gain insight into the phenomena that determine knock onset, detected by an external microphone. In particular, the study examines how the end-gas autoignition process changes as the engine's spark timing is advanced through the borderline knock limit into the engine's knocking regime. Fast Fourier transforms (FFT) and bandpass filtering techniques were used to process the recorded cylinder pressure data to determine knock intensities for each cycle. Two characteristic pressure oscillation frequencies were detected: a peak just above 6 kHz and a range of peaks in the 15-22 kHz range. The microphone data shows that the audible knock signal has the same 6 kHz peak.

This paper presents tribological modeling, experimental work, and validation of tribology parameters of a single cylinder turbocharged diesel engine run at various loads, speeds, intake boost pressures, and cylinder liner temperatures. Analysis were made on piston rings and liner materials, rings mechanical and thermal loads, contact pressure between rings and liner, and lubricant conditions. The engine tribology parameters were measured, and used to validate the engine tribology models. These tribology parameters are: oil film thickness, coefficient of friction between rings and liner, friction force, friction power, friction torque, shear rate, shear stress and wear of the sliding surfaces. In order to measure the oil film thickness between rings and liner, a single cylinder AVL turbocharged diesel engine was instrumented to accept the difference in voltage drop method between rings, oil film, and liner.

The presence of liquid fuel inside the engine cylinder is believed to be a strong contributor to the high levels of hydrocarbon emissions from spark ignition (SI) engines during the warm-up period. Quantifying and determining the fate of the liquid fuel that enters the cylinder is the first step in understanding the process of emissions formation. This work uses planar laser induced fluorescence (PLIF) to visualize the liquid fuel present in the cylinder. The fluorescing compounds in indolene, and mixtures of iso-octane with dopants of different boiling points (acetone and 3-pentanone) were used to trace the behavior of different volatility components. Images were taken of three different planes through the engine intersecting the intake valve region. A closed valve fuel injection strategy was used, as this is the strategy most commonly used in practice. Background subtraction and masking were both performed to reduce the effect of any spurious fluorescence.

This paper explores the combined effects of boosting, intake air temperature, trapped residual gas fraction, and dilution on the Maximum Pressure Rise Rate (MPRR) in a boosted single cylinder gasoline HCCI engine with combustion controlled by negative valve overlap. Dilutions by both air and by cooled EGR were used. Because of the sensitivity of MPRR to boost, the MPRR constrained maximum load (as measured by the NIMEP) did not necessarily increase with boosting. At the same intake temperature and trapped residual gas fraction, dilution by recirculated burn gas was effective in reducing the MPRR, but dilution by air increased the value of MPRR. The dependence of MPRR on the operating condition was interpreted successfully by a simple thermodynamic analysis that related the MPRR value to the volumetric heat release rate.

Hydrogen can be readily used in spark-ignition engines as a clean alternative to fossil fuels. However, a larger burning velocity and a shorter quenching distance for hydrogen as compared with hydrocarbons bring a larger cooling loss from burning gas to the combustion-chamber wall. Because of the large cooling loss, the thermal efficiency of a hydrogen-fueled engine is sometimes lower than that of a conventionally fueled engine. Therefore, the reduction of the cooling loss is very important for improving the thermal efficiency in hydrogen-combustion engines. On the other hand, the direct-injection stratified charge can suppress knocking in spark-ignition engines at near stoichiometric overall mixture conditions. Because this is attributed to a leaner end gas, the stratification can lead to a lowered temperature of burning gas around the wall and a reduced cooling loss.

In one dimensional engine simulation software, flow losses over complex geometries such as valves and ports are described using flow coefficients. It is generally assumed that the pressure ratio over the valve has a negligible influence on the flow coefficient. However during the exhaust valve opening the pressure difference between cylinder and port is large which questions the accuracy of this assumption. In this work the influence of pressure ratio on the exhaust valve flow coefficient has been investigated experimentally in a steady-flow test bench. Two cylinder heads, designated A and B, from a Heavy-Duty engine with different valve shapes and valve seat angles have been investigated. The tests were performed with both exhaust valves open and with only one of the two exhaust valves open. The pressure ratio over the exhaust port was varied from 1.1:1 to 5:1. For case A1 with a single exhaust valve open, the flow coefficient decreased significantly with pressure ratio.

The piston’s skirt shape is a key design parameter since it critically influences lateral displacement, tilting movement, oil transport and consequently engine performances. This study proposes an alternative skirt profile that aims to reduce frictional losses between the piston and cylinder liner. Qualitatively, the proposed profile, aims to reduce solid-to-solid contact friction by increasing the total hydrodynamic forces generated on the skirt to balance side forces, and to prevent both sides of the skirt to interact with the liner simultaneously. The new skirt’s profile has been first studied and optimized using a piston secondary motion model and then prototyped and tested on a floating liner test bench, showing a 12% average reduction in total piston FMEP.

The increasingly stringent regulations for fuel economy and emissions require better optimization and control of oil consumption. One of the primary mechanisms of oil consumption is vaporization from the liner; we consider this as the “minimum oil consumption (MOC).” This paper presents a physical-mathematical cycle model for predicting the MOC. The numerical simulations suggest that the MOC is markedly sensitive to oil volatility, liner temperature, engine load and speed but less sensitive to oil film thickness. A one-line correlation is proposed for quick MOC estimations. It is shown to have <15% error compared to the cycle MOC computation. In the “dry region” (between top ring and OCR at the TDC), oil is depleted due to high heat and continual exposure to the combustion chamber.

An experimental study was performed in a firing SI engine at conditions representative of the warmup phase of operation in which liquid gasoline films were established at various locations in the combustion chamber and the resulting impact on hydrocarbon emissions was assessed. Unique about this study was that it combined, in a firing engine environment, direct visual observation of the liquid fuel films, measurements of the temperatures these films were subjected to, and the determination from gas analyzers of burned and unburned fuel quantities exiting the combustion chamber - all with cycle-level resolution or better. A means of deducing the exhaust hydrocarbon emissions that were due to the liquid fuel films in the combustion chamber was developed. An increase in exhaust hydrocarbon emissions was always observed with liquid fuel films present in the combustion chamber.

A twin-land oil control ring (TLOCR) model is used to evaluate TLOCR friction and the results are compared to the experiment measurement in a single cylinder floating liner engine under motoring condition. The model is based on a correlation between the hydrodynamic pressure and film thickness, which is generated using a deterministic model. The well-known three-regime lubrication is predicted with the model for ring with different ring tensions under various engine running conditions. A good match is found for the model and experiment results.

The objective of this work was to develop an experimental system to support development and validation of a model for the lubrication of two-piece Twin-Land-Oil-Control-Rings (hereafter mentioned as TLOCR). To do so, a floating liner engine was modified by opening the head and crankcase. Additionally, only TLOCR was installed together with a piston that has 100 micron cold clearance to minimize the contribution of the skirt to total friction. Friction traces, FMEP trend, and repeatability have been examined to guarantee the reliability of the experiment results. Then, engine speed, liner temperature, ring tension, and land widths were changed in a wide range to ensure all three lubrication regimes were covered in the experiments.

Modern spark-ignited (SI) engines offer excellent emission reduction when operated with a stoichiometric mixture and a three-way catalytic converter. A challenge with stoichiometric compared to diluted operation is the knock propensity due to the high reactivity of the mixture. This limits the compression ratio, thus reducing engine efficiency and increasing exhaust temperature. The current work evaluated a model of conditions at inlet valve closing (IVC) and top dead center (TDC) for steady state operation. The IVC temperature model is achieved by a cycle-to-cycle resolved residual gas fraction estimator. Due to the potential charge cooling effect from methanol, a method was proposed to determine the fraction of fuel sourced from a wall film. Determining the level of charge cooling is important as it heavily impacts the IVC and TDC temperatures.