Search Results

A three-dimensional combustion model for a direct-injection stratified-charge rotary engine is used to identify modifications to the engine that should lead to better indicated efficiency. The engine has a single spark plug positioned alongside a single-hole pilot injector in a cavity located after the minor axis and a five-hole main injector that is located before the minor axis. It is predicted that a second ignition source located upstream of the main injector will lead to an increase in indicated efficiency of 6-8% if it ignites the mixture consistently. The computations were made at high and low engine speeds and loads, covering a significant part of the practical operating range of the engine. It is also predicted that the gain in efficiency of the engine with two ignition sources would be 7-10%, instead of 6-8%, if a two-hole pilot injector is also used instead of the one-hole pilot.

A sheet of laser light from a frequency tripled Nd-YAG laser approximately 200μm thick is shone through the combustion chamber of a single cylinder, direct injection internal combustion engine. The injected decane contains exciplex—forming dopants which produce spectrally separated fluorescence from the liquid and vapor phases. The fluorescence signal is collected through a quartz window in the cylinder head and is imaged onto a diode array camera. The camera is interfaced to a microcomputer for data acquisition and processing. The laser and camera are synchronized with the crankshaft of the engine so that 2—D images of the liquid and vapor phase fuel distributions can be obtained at different times during the engine cycle. Results are presented at 600, 1200 and 1800 rpm, and from the beginning to just after the end of injection. The liquid fuel traverses the cylinder in a straight line in the form of a narrow cone, but does not reach the far wall in the plane of the laser sheet.

Lateral integral length scales of the tangential velocity component were measured directly using a two-point, single probe—volume, Laser Doppler Velocimetry system in a motored, ported, single-cylinder I.C. engine with a pancake—shaped chamber. The measurements were made on the mid-plane of the TDC clearance height from 40 degrees before TDC to 25 degrees after TDC. The engine was operated at 600 rpm with a swirl ratio at TDC of approximately 4. Both an ensemble and a cycle-resolved statistical analysis were performed. Three compression ratios (5.7, 7.6, and 11.4) were used. They correspond to TDC clearance heights of 18.1 mm, 12.8 mm, and 8.2 mm, respectively. Contrary to expectations, both the lateral turbulence integral length scale (deduced from the cycle-resolved analysis) and the lateral fluctuation integral length scale (deduced from simple ensemble averaging) did not scale with TDC clearance height, but rather were almost independent of it around TDC.

Studies are reported of stratified-charge combustion in rotary engines. They were performed with a three-dimensional model that computes intake, compression, liquid fuel injection, combustion, expansion, and exhaust. Comparisons are shown of computed and measured chamber pressures for two engines and seven conditions. They are the first comparisons of three-dimensional computations for rotary engines. The agreement is adequate for the purpose of interpreting the main features of the combustion flowfield. Then two subjects are considered: the mixing of injected-fuel and air, and the pressure non-uniformity within the combustion chamber. It is found that the TDC turbulence diffusivity of rotary engines in general is smaller than in corresponding reciprocating engines because of the longer time between intake and TDC. The pressure non-uniformity is shown to be caused by large fluid acceleration around TDC.

The first comparisons of measured and computed mean velocities, and of measured fluctuation intensities and computed turbulence intensities in a motored rotary engine are presented. The computations were performed with a recently developed three–dimensional model. The measurements were made at the Sandia National Laboratories by Dimpelfeld and Witze at several locations along the rotor housing and at two engine speeds. The measured and computed mean velocities agree to within 15% whereas the computed turbulence intensities correctly are lower than the measured fluctuation intensities by about 30% to 50%, as anticipated. Under motored conditions, the turbulence intensity tends to be rather homogeneous and of similar magnitude somewhat before and after top dead center but significantly inhomogeneous and of greater magnitude around top dead center. The comparisons suggest that predictions of mean gas velocity and of turbulence intensity can be made with the available model.

The three components of the velocity were measured by laser Doppler velocimetry at 35 locations in each of the six intake ports of a single-cylinder I.C. engine motored at 600, 900, and 1200 rpm. The intake ports were designed to impart both swirl and roll to the air. Pressure was also measured at the intake and exhaust. The detailed information is valuable mostly for computations of engine flows and for the assessment of multidimensional models. However the following trends were observed. The intake velocity is affected by resonant pressure waves. The flows in the six ports tend to be similar. The three components of the ensemble-averaged velocity generally have uniform profiles across the port area, whereas the fluctuation intensities are higher at the top of the port. All velocities tend to be higher at the beginning and end of intake.