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The purpose of this research was to measure and correlate the area-average heat transfer coefficients for free, circular upward-impinging oil-jets onto two automotive pistons having different undercrown shapes and different diameters. For the piston heat transfer studies, two empirical area-average Nusselt number correlations were developed. One was based on the whole piston undercrown surface area with the Nusselt number based on the nozzle diameter, and the other was based on the oil-jet impingement area with the Nusselt number based on the oil-jet effective impingement diameter. The correlations can predict the 95% and 94% of the experimental measurements within 30% error, respectively. The first correlation is simpler to use and can be employed for cases in which the oil jet wets the whole piston undercrown. The latter may be more useful for larger pistons or higher Prandtl number conditions in which the oil jet wets only a portion of the undercrown.

In this paper, we develop a methodology to enable the isolation of the heat release contribution of knocking combustion from flame-propagation combustion. We first address the empirical modeling of individual non-autoigniting combustion history using the Wiebe function, and subsequently apply this methodology to investigate the effect of autoignition on the heat release history of knocking cycles in a spark ignition (SI) engine. We start by re-visiting the Wiebe function, which is widely used to model empirically mass burned histories in SI engines. We propose a method to tune the parameters of the Wiebe function on a cycle-by-cycle basis, i.e., generating a different Wiebe to suitably fit the heat release history of each cycle. Using non-autoigniting cycles, we show that the Wiebe function can reliably simulate the heat release history of an entire cycle, if only data from the first portion of the cycle is used in the tuning process.

Experiments were carried out on a straight pipe extension of an exhaust port of a multi-cylinder, spark-ignition engine to investigate the axial variation of the steady-state surface heat transfer. Local, steady-state, surface heat flux measurements were made at five different stations on the test section. Based on an optimization procedure developed in this study, the heat-flux measurements obtained for axial distances x / D > 2, were found to be correlated very well (R2 = 0.95) by an equation in the form of an entrance length correction, which is a function solely of x / D, multiplied by the Sieder-Tate convective heat transfer correlation; a correlation valid for fully-developed, steady-state, turbulent, pipe flows. Most importantly, this paper provides strong evidence that the observed heat transfer augmentation in the engine exhaust system is due solely to entrance effects and not due to flow fluctuations, which was the accepted cause.

This study examines the contributions and interactions of intake and exhaust tuning on a 4-stroke single-cylinder engine for various engine speeds and valve timings. The parametric study was performed using a 1-D engine simulation model, the combustion sub-model of which was calibrated based on experimental pressure data. Mechanisms by which tuning changes the volumetric efficiency of an engine were studied. Simulation results are compared with established empirical correlations which predict pipe lengths for maximum volumetric efficiency. It was found that intake tuning has a more dominant role in the breathing capability of the engine compared to exhaust tuning and that both are independent from each other. Valve timing was found to have no effect on intake tuning characteristics but to affect exhaust tuning.

In this paper, we investigate the effects of autoignition on the heat release characteristics of a spark-ignition (SI) engine, under knocking conditions. In a normal, flame-propagation combustion, the heat release rate increases smoothly to a maximum, and then progressively decreases as the entire mixture is consumed. When autoignition occurs, the heat release rate profile shows a departure from its normal profile: since autoignition results in an explosive combustion, an abnormal rapid increase in heat release rate is generated, with significantly higher peak heat release rates and faster fuel consumption. Three distinct heat-release-rate profiles for autoignition can be identified at different engine speeds, which differ in the phasing of the sudden increase in release rate due to autoignition, relative to the peak release rate due to normal combustion.

This paper presents an experimental study of the cycle-averaged, local surface heat transfer, from the exhaust gases to a straight pipe extension of the exhaust port of a four-cylinder spark-ignition (SI) engine, over a wide range of engine operating conditions, from 1000 rpm, light load, through 4000 rpm, full load. The local steady-state heat flux was well correlated by a Nusselt-Reynolds number relationship that included entrance effects. These effects were found to be the major contributor to the local heat transfer augmentation. The Convective Augmentation Factor (CAF), which is defined as the ratio of the measured heat flux to the corresponding heat flux for fully-developed turbulent pipe flow, was found to decrease with increasing Reynolds number and increasing axial distance from the entrance of the test section.

This study employs experimental and computational methods to investigate the thermal state of the exhaust manifold of a multi-cylinder turbocharged diesel engine operating under steady-state conditions. The local skin temperatures and surface heat fluxes varied significantly throughout the external surface of the manifold. The augmentation of the local heat flux with increasing load and engine speed may be represented solely by the increase in the fuel mass flow rate. The results of the 1D simulation are in good agreement with the measurements of the exit gas temperatures, skin temperatures, and surface heat fluxes.

This work describes an experimental investigation on the stratified combustion and engine-out emissions characteristics of a single-cylinder, spark-ignition, direct-injection, spray-guided engine employing an outward-opening injector, an optimized high-squish, bowled piston, and a variable swirl valve control. Experiments were performed using two different outward-opening injectors with 80° and 90° spray angles, each having a variable injector pintle-lift control allowing different rates of injection. The fuel consumption of the engine was found to improve with decreasing air-swirl motion, increasing spark-plug length, increasing spark energy, and decreasing effective rate of injection, but to be relatively insensitive to fuel-rail pressure in the range of 10-20 MPa. At optimal injection and ignition timings, no misfires were observed in 30,000 consecutive cycles.

This paper is a continuation of an earlier paper, which examined the steady-state internal heat transfer in the exhaust system of a diesel powered, light-duty vehicle. The present paper deals with the heat transfer of the exhaust system during two types of transient testing, as well as, the estimation of the exhaust systems external heat transfer. Transient heat transfer was evaluated using: a simple fuel-step transient under constant speed and the New European Driving Cycle (NEDC). The thermal response of the external walls varied considerably for the various components of the exhaust system. The largest percent difference between the measured temperatures and the corresponding quasi-steady estimates were about 10%, which is attributed to thermal storage. Allowing for thermal storage resulted in an excellent agreement between measurements and analysis.

A methodology was developed, based on engine-simulation analysis and experiments, to evaluate quantitatively the contributions of the various factors on the fuel-economy advantage of direct-injection, spark-ignition (DISI) engines over corresponding port-fuel injection (PFI) engines. The fuel-economy comparison was based on a set of seven, steady-state test points, which simulate a 2400-kg vehicle powered by a 5.3-L V8 engine over the Federal Test Procedure (city cycle). The results show that the DISI engine has a 15% fuel-economy advantage over the corresponding PFI engine operating without EGR. The biggest positive contributor to this gain is the reduced pumping losses, which account for a 10% gain, followed by: favorable mixture properties due to lean/dilute operation with about a 7.5% gain, lower heat losses with a 2% gain, and higher compression ratio with a 3% gain.

This study is an experimental and computational investigation of the influence of injection timing, fuel spray orientation, and in-cylinder air motion on the combustion, fuel economy, and engine-out emissions of a single-cylinder, 2-valve, spark-ignition direct-injection (SIDI) engine, operating under stratified-charged conditions. For the best compromise between fuel consumption, combustion stability, engine-out hydrocarbon emissions and smoke, the engine required relatively retarded injection timings (in comparison to other charge- or wall-controlled DI engines), high swirl levels, and a spray orientation that is directed towards the intake-valve side and targets the ridge wall of the piston.

The present study is an experimental investigation on the influence of engine operational parameters on the temperature history of intake valves. During the initial stage of the warm-up process, the temperature history of the intake valve followed an exponential behavior with a time constant that ranged from about 23 to 39 s for the test conditions examined. In contrast, the temperature history of the coolant varied linearly with time suggesting that the net heat input to the coolant is roughly constant during the initial stage of the engine warm-up process. After the initial transient phase that lasted about one minute, the temperature rise of the intake valve was quasi-steady. During this latter period, the measured intake valve temperature was predicted by the steady-state temperature correlation developed in an earlier study.