A spark plug calorimeter is introduced for quantifying the thermal energy delivered to unreactive gas surrounding the spark gap during spark ignition. Unlike other calorimeters, which measure the small pressure rise of the gas above the relatively high gauge pressure or relative to an internal reference, the present calorimeter measured the differential rise in pressure relative to the initial pressure in the calorimeter chamber. By using a large portion of the dynamic range of the chip-based pressure sensor, a high signal to noise ratio is possible; this can be advantageous, particularly for high initial pressures. Using this calorimeter, a parametric study was carried out, measuring the thermal energy deposition in the gas and the electrical-to-thermal energy conversion efficiency over a larger range of initial pressures than has been carried out previously (1–24 bar absolute at 298 K). The spark plug and inductive ignition circuit used gave arc-type rather than glow-type discharges. A standard resistor-type automotive spark plug was tested. The effects of spark gap distance (0.3–1.5 mm) and ignition dwell time (2–6 ms) were studied for an inductive-type ignition system. It was found that energy deposition to the gas (nitrogen) and the electrical-to-thermal energy conversion efficiency increased strongly with increasing gas pressure and spark gap distance. For the same ignition hardware and operating conditions, the thermal energy delivered to the gap varied from less than 1 mJ at 1 atm pressure and a gap distance of 0.3 mm to over 25 mJ at a pressure of 24 bar and a gap distance of 1.5 mm. For gas densities that might be representative of those in an engine at the time of ignition, the electrical-to-thermal energy conversion efficiencies ranged from approximately 3% at low pressures (4 bar) and small gap (0.3 mm) to as much as 40% at the highest pressure of 24 bar and with a gap of 1.5 mm.

Intake throttling has been verified as an effective approach to increase the exhaust temperature of diesel engines, which could benefit the catalytic efficiency aftertreatment. To better understand the influence of intake throttling on the combustion characteristics and exhaust emissions of light-duty diesel engines operating under idle mode, a light-duty diesel engine was experimentally investigated. This study is a follow-on to previous studies on the effect of throttling on light-duty diesel engine exhaust temperatures and emissions. Tests were conducted at a fixed idle speed of 1100 rpm, and the throttle position and intake manifold air pressure (MAP) were varied. The in-cylinder pressure, pressure rise rate, heat release rate (HRR), in-cylinder temperature, exhaust temperature, and regular gaseous emissions were analyzed. The results indicated that under the influence of intake throttling, the MAP decreased from 101 kPa under wide-open-throttle (WOT) conditions to 52.5 kPa under the heaviest throttling conditions, and the exhaust temperature increased from 100 °C to 200 °C, with a fuel penalty associated with the increase in the pumping indicated mean effective pressure (IMEP). The in-cylinder pressure continuously declined with decreasing MAP, while the HRR generally increased with increasing MAP. Under WOT conditions, the ignition delay decreased, while the combustion duration decreased under heavier throttling conditions. The in-cylinder temperature with throttling was higher than that under WOT conditions, and after post-injection treatment, the in-cylinder temperature exhibited an increasing trend with decreasing MAP. The CO₂, CO, NO_x, and HC emissions increased with increasing throttling amounts.

The Rotating Liner Engine (RLE) concept is a design concept for internal combustion engines, where the cylinder liner rotates at a surface speed of 2–4 m/s in order to assist piston ring lubrication. Specifically, we have evidence from prior art and from our own research that the above rotation has the potential to eliminate the metal-to-metal contact/boundary friction that exists close to the piston reversal areas. This frictional source becomes a significant energy loss, especially in the compression/expansion part of the cycle, when the gas pressure that loads the piston rings and skirts is high. This paper describes the Diesel RLE prototype constructed from a Cummins 4BT and the preliminary observations from initial low load testing. The critical technical challenge, namely the rotating liner face seal, appears to be operating with negligible gas leakage and within the hydrodynamic lubrication regime for the loads tested (peak cylinder pressures of the order of 100 bar) and up to about 10 bar BMEP (brake mean effective pressure). Preliminary testing has proven that the metal-to-metal contact in the piston assembly mostly vanished, and a friction reduction at idle conditions of about 40% as extrapolated to a complete engine has taken place. It is expected that as the speed increases, the friction reduction percentage will diminish, but as the load increases, the friction reduction will increase. The fuel economy benefit over the US Heavy-Duty driving cycle will likely be of the order of 10% compared to a standard engine.