## 3 Testing the RLE and BSL Single Cylinder Engines under Idle Conditions
### BSL Testing under Reduced Compression Ratio  
We decided to conduct a few more tests with the BSL and obtain some preliminary CO2 exhaust concentrations from it. The BSL revival was performed without the crankshaft encoder, since we did not want to move this from the RLE and upset our TDC position. However, we could still take cylinder pressure data via the oscilloscope, which are presented in this subsection. Prior to reviving the BSL, we also decided to reduce its compression ratio, so it would be a better match to the RLE; the correction factor due to differences in clearance volume would hopefully become 1 or closer to 1. As it turned out, the compression ratio of the BSL became slightly lower, so the correction factor was still needed, but the correction factor now amplified the difference in PCP-PMP rather than reducing it. The variation of compression ratio was performed by replacing the original thick copper head gasket with  
Figure 13: (**a**) Pressure vs. crank angle history on the RLE when the timing is retarded. Note that combustion is still fairly fast compared to BSL Case 3 (see Appendix A), but we can still consider this a close comparable case for PCP-PMP comparison. (**b**) Pressure vs. volume for the RLE in the retarded condition. Note that now the premixed combustion is right at the TDC with some significant heat release occurring past the TDC, which lowers PCP. This is to be contrasted against Figure 12b, where the premixed combustion is well before the TDC, and only a slight amount of heat is released before the TDC, or Figure 11 (red), where all the heat is released well before TDC. a stock gasket, but apparently, given that we did not know exactly the extent to which each gasket crushes, the compression ratio did not end up at the exact value of the RLE (we used a copper head gasket in the RLE as well, but the head bolts were torqued down to a lower torque than the BSL, since the combustion gases were contained by our RLE hydrodynamic face seal). The compression ratio comparison was performed via our motoring test. This motoring test is not exactly a motoring test, since we do not have a motoring dynamometer. Instead, we rev the engines up, turn off the injection pump, and record pressure and speed. This can be conducted with the data acquisition system, or simply by the oscilloscope. This process is shown in the Appendix A. The process yielded 28 bar absolute (27 bar gage) at around 1080 rpm (the sensitivity of the peak pressure on rpm is very low for both engines; it used to be slightly more pronounced for the BSL when it operated with a higher compression ratio). The comparison in terms of CO2 concentration is shown in Tables 1 and 2. Comparing the cases with advanced injection timing, the RLE exhibited about 20% lower CO2 concentration for the idle condition in question. With the retarded timing, the difference became substantially wider at a 45% difference. This margin is larger than the pressure data suggest, and we cannot explain this large difference yet. During these tests, it was discovered that some further correlations between PCP-PMP can be made, and the injection timing can be used as a variable. Specifically, we know that as the injection timing is retarded, the PCP will be reduced. We wanted to capture this effect and compare it to how the RLE responds to similar injection timing. This allowed us to group cases with similar combustion characteristics, and make more refined comparisons, thus eliminating the uncertainty of injection timing. Even though we can no longer define the exact position of the premixed combustion with respect to the TDC (given the absence of the crankshaft encoder from the BSL), the changes in the combustion characteristics are fairly large, and solid conclusions can be made, even in the absence of an encoder. In this next series of experiments, the new injector with reduced cracking pressure was used with the BSL as was the case of the RLE data given in Figure 12b. In this case, it has a rather advanced injection timing.