Piston Engines - Introduction — Page 15, Lesson 17

We're starting the Piston Engines chapter, and the very first thing on the table is a reference table of terms and formulae. This is your foundation—every calculation we do later in this chapter and in the next ones pulls from this list. So let's go through it line by line, because you'll need these cold. First, electrical quantities. Potential Difference, symbol V, measured in Volts. The formula is V = IR — that's voltage equals current times resistance. Next, Current, symbol I, in Amperes, and it's I = V/R. Then Resistance, symbol R, in Ohms, the Greek letter omega, and R = V/I. These three are Ohm's law rearranged three ways. Then Power, symbol P, in Watts. Two formulas here: P = V × I, or equivalently P = I²R. Both are the same thing expressed differently. Now mechanical quantities. Force, symbol F, in Newtons — and note the alternative unit, pounds force, lbf. The formula is F = ma, force equals mass times acceleration. Mass, symbol m, in kilograms or pounds, and it appears in the same formula, F = ma. Density, symbol ρ — that's the Greek letter rho — in kg/m³ or lb/ft³. Density is ρ = m/V, mass divided by volume. Careful: that V here is volume, not voltage. Moment, symbol M, in Newton Metres or pounds feet. A moment is a turning effect, and it's M = F × d, force times distance. Velocity, symbol v, in metres per second or feet per second, and it's v = d/t, distance divided by time. Acceleration, symbol a, in m/sec² or ft/sec², and it's a = F/m — acceleration equals force over mass. Pressure, symbol P, in Pascals — and note a Pascal is a N/m² — or lb/in². Pressure is P = F/A, force divided by area. Area, symbol A, in m² or in², and it's A = F/P, the inverse. Then Volume, in m³ or ft³ — no formula given, it's a base quantity. Frequency, in Hertz, which is cycles per second. Work Done, in Joules or ft lb, and it's Wd = F × d — force times distance, same shape as moment but conceptually different. Potential Energy, symbol PE, in Joules, and it's PE = m × g × h — mass times gravitational acceleration times height. Kinetic Energy, in Joules, and it's KE = ½mv² — half mass times velocity squared. Finally, Efficiency. No symbol, no unit — it's a ratio: useful work output divided by total energy input. That's the definition you'll carry through the whole engine performance discussion. Now, the chapter outline that follows tells you where we're headed. We'll cover Engine Layout, then the Theoretical Otto Cycle and its operation, then the Practical Otto Cycle — that's the real four-stroke sequence. After that: Power to Weight Ratio, Specific Fuel Consumption (SFC), Engine Efficiencies, Compression Ratio, and then the mechanical construction — Crankcase, Crankshaft (also called the cranked-shaft), Connecting Rods, Pistons, Cylinder Barrel or Block, Cylinder Head, Valve Operating Gear, and Valve Clearance. That's the roadmap. We'll start with the layout and the Otto cycle next.