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Fast emissions analysis, soot analysis, and pressure sensing is utilized to examine the first few seconds before, and after startup in a single-cylinder CFR diesel engine. The equivalence ratio, compression ratio, and injection timing are varied. The data show that UHC and CO emissions are highest at the highest and lowest fueling conditions, while NOx emissions peaked at intermediate fueling conditions. Leaner operating conditions show delayed starting but reduced ignition delay. Oil vapor causes soot emissions prior to first combustion, and soot particle size shifts higher during the first few seconds after combustion begins. Injection timing has little effect except at the leanest equivalence ratios, where a retarded injection timing increases the delay until a successful combustion event. At lower compression ratios, large IMEP oscillations occurred during startup. The data suggest possible strategies to optimize diesel startup.