Greensteam

As the Engine Team Lead, I was responsible for mentoring 3 students, conducting research and design relating to power generation from steam, and writing research reports and grant proposals.

2021 UCI Undergraduate Research Symposium

Reciprocating Engines

Cam-actuated Uniflow Boxer Engine

This engine has two diametrically opposed cylinders with corresponding pistons that are connected by a scotch yoke. Since this engine utilizes uniflow exhaust and the cylinders are opposite each other, one cylinder is always in a power stroke while the other is in its return stroke. A flywheel is necessary to ensure smooth running at top and bottom dead center. An overhung crank has been implemented in the design to drive the scotch yoke, since traditional crank shafts are very difficult to manufacture and require extreme precision. Inlet valve actuation is accomplished by 2 spool valves driven by a cam attached to the shaft.

Disk-actuated Triradial Engine

This engine has a triradial layout meaning the 3 cylinders are spaced equally 120° apart around the shaft. Each cylinder is offset slightly from the others so the piston rods may all attach to the same overhung crank. Behind the cylinders, the shaft drives 2 thin disks, on each side of the main plate, which act as the exhaust and inlet valves. Each disk has a slot--the shape of which determines timing and flow rate--which allows exhaust to escape to the atmosphere and inlet steam to enter the cylinders, both through milled manifolds in the main plate. The disks are forced to rotate with the shaft due to the key/keyway mechanism, but are not fixed for translational movement so that they may be pressure sealed against the plate. The advantage of this triradial cylinder layout is that the engine is able to run smoothly without requiring a flywheel. The 2 disks do the same work as 6 traditional poppet-type valves, vastly reducing the number of moving parts but also raising new concerns for sealing. Sealing between the disk and the manifold plate is accomplished by the pressure of the inlet steam itself which pushes against the disk (much like the sliding D valve mechanism). While the pressure addresses sealing, it also creates a large amount of friction, so the disk and plate will have to be heavily lubricated or plated with a low-friction material such as Teflon.

Double-acting Uniflow Compound Engine

This is a 2 stage double-acting inline compound engine. This engine replaces the traditional cross-slide by extending the piston rod through the back end of the cylinder, thereby supporting the piston on either end. This increases the amount of required seals by two, but reduces moving mass and engine complexity. Steam enters the high pressure cylinder on both ends through bash valves. After high pressure expansion, steam exits through uniflow ports into a manifold which goes to the low pressure cylinder. Here, the semi-expanded steam expands again before finally exiting through uniflow exhaust ports into the atmosphere. The timing between high and low pressure pistons is slightly offset such that for the first ~5-10% of low pressure power stroke, the low pressure piston acts as a pump to improve the exhaust performance of the high pressure cylinder. For this portion, the low pressure piston is actually doing negative work, but the hope is that this produces more efficiency gains in the exhaust process to offset these losses. This claim is not too far-fetched considering, for example, internal combustion engines also incorporate an exhaust stroke in which the piston acts as a pump to remove the exhaust gas. Of course, this mechanism will need to be validated with further calculations.

Tube-actuated Dual-Inline Engine

This engine has 2 cylinders, one on either side of a central flywheel. 2 overhung cranks drive the cylinders, diametrically opposed so that while one piston is in power stroke the other is in return stroke. This layout is akin to that of a bicycle, where the 2 pistons are the cyclist’s legs which force the pedals (overhung cranks) to rotate. Since there are 2 overhung cranks, no side of the shaft is free to act as the output driveshaft, so the flywheel also acts as a pulley which links with an external driveshaft.  There are 2 rotating hollow pipes that run below the head of the cylinders, parallel to the crankshaft, and act as the inlet and exhaust valves. These pipes are linked to the crankshaft via a timing belt. The inlet tube is fed a constant supply of steam from one side and sealed on the other, while the exhaust tube is open on both sides to atmospheric pressure. Both pipes each have 2 slotted cuts that open into the cylinders for a period which determines timing for inlet, expansion, exhaust, and compression. The benefit of this valve system is that the 2 pipes essentially replace the need for 4 valves, reducing the number of moving parts while maintaining perfect control over valve timing. The drawback is that there are concerns with sealing between the pipes and their bores which could result in leakage between cylinders. Additionally, thermal expansion of the pipes must be taken into account when determining clearance so as to prevent the pipes from seizing in the cylinder block.